6 Reworded second paragraph for smoother flow.
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As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from get Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum (first & second contain the pertinent ""Losers tournamentLosers tournament" contains the pertinent tables, while the third & fourth pages of that thread contain two tables for their "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).

Sequenced in accordance with the engines' normalized mean averages of those tournaments:

As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum (first & second contain the pertinent "Losers tournament" tables, the third & fourth contain tables for "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).

Sequenced in accordance with the engines' normalized mean averages:

As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from get Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum ("Losers tournament" contains the pertinent tables, while the third & fourth pages of that thread contain two tables for their "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).

Sequenced in accordance with the engines' normalized mean averages of those tournaments:

5 Added PyChess for reference purposes; deleted note-letters' quotation marks while I was at it.
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As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum (first & second contain the pertinent "Losers tournament" tables, the third & fourthfourth contain tables for "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).

  1. Sjeng 11.2  . . . . . . . . . . . . . . . . . . . . . . . . . 0.885416(7)

  2. Olithink 2.2.1 [OliPow] note "A"A   . . . . . . . . . 0.5625(0)

  3. Pulsar 2009-9b  . . . . . . . . . . . . . . . . . . . . . 0.411458(3)

  4. Gerbil 02 note "B"B    . . . . . . . . . . . . . . . . . . . . 0.3541(6)

  5. KKF 2.6.6 . . . . . . . . . . . . . . . . . . . . . . . . . . 0.31708(3)

  6. Nebiyu 1.41 notes "C[C.x]"x . . . . . . . . . . . . . . . . UNDEF. (0.275(+), est.)

  7. PyChess note D  . . . . . . . . . . . . . . . . . . . . UNDEF.

  • A: multiple other versions of OliThink 2.2.1 (in addition to those in the normalized list's link) can be had elsewhere (at the bottom, in the “Older versions:” section).

  • B: Gerbil ver.s 01 & 02 "...come with a separate executable for loser's chess...".

  • C: Nebiyu Alien has many additional [user defined] .ini files available as a collective package or individually.

  • C.1: Nebiyu can play Losers Chess, if you edit the winboard.ini (after which, “With -W (w17) [in the command line option] losers chess it works fine...”).

  • C.2: Note that Nebiyu might be “...playing atomic losers chess.” (later attested to the contrary by another).

  • D: PyChess wasn't one of the competitors, but can play Losers Chess, though it might be too weak an engine (in context of Losers Chess) to consider modifying for this purpose.

As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum (first & second contain the pertinent "Losers tournament" tables, the third & fourth contain tables for "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).

  1. Sjeng 11.2  . . . . . . . . . . . . . . . . . . . . . . . . . 0.885416(7)

  2. Olithink 2.2.1 [OliPow] note "A" . . . . . . . . 0.5625(0)

  3. Pulsar 2009-9b  . . . . . . . . . . . . . . . . . . . . . 0.411458(3)

  4. Gerbil 02 note "B"    . . . . . . . . . . . . . . . . . . 0.3541(6)

  5. KKF 2.6.6 . . . . . . . . . . . . . . . . . . . . . . . . . . 0.31708(3)

  6. Nebiyu 1.41 notes "C[.x]" . . . . . . . . . . . . . UNDEF. (0.275(+), est.)

As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum (first & second contain the pertinent "Losers tournament" tables, the third & fourth contain tables for "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).

  1. Sjeng 11.2  . . . . . . . . . . . . . . . . . . . . . . . . . 0.885416(7)

  2. Olithink 2.2.1 [OliPow] note A   . . . . . . . . . 0.5625(0)

  3. Pulsar 2009-9b  . . . . . . . . . . . . . . . . . . . . . 0.411458(3)

  4. Gerbil 02 note B  . . . . . . . . . . . . . . . . . . . . 0.3541(6)

  5. KKF 2.6.6 . . . . . . . . . . . . . . . . . . . . . . . . . . 0.31708(3)

  6. Nebiyu 1.41 notes C.x . . . . . . . . . . . . . . . . UNDEF. (0.275(+), est.)

  7. PyChess note D  . . . . . . . . . . . . . . . . . . . . UNDEF.

  • A: multiple other versions of OliThink 2.2.1 (in addition to those in the normalized list's link) can be had elsewhere (at the bottom, in the “Older versions:” section).

  • B: Gerbil ver.s 01 & 02 "...come with a separate executable for loser's chess...".

  • C: Nebiyu Alien has many additional [user defined] .ini files available as a collective package or individually.

  • C.1: Nebiyu can play Losers Chess, if you edit the winboard.ini (after which, “With -W (w17) [in the command line option] losers chess it works fine...”).

  • C.2: Note that Nebiyu might be “...playing atomic losers chess.” (later attested to the contrary by another).

  • D: PyChess wasn't one of the competitors, but can play Losers Chess, though it might be too weak an engine (in context of Losers Chess) to consider modifying for this purpose.

4 Removed extraneous quotation mark, modified last entry to "+" rather than "0" (due to margin of uncertainty).
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As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum (first & second contain the pertinent "Losers tournament"tournament" tables, the third & fourth contain tables for "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).

  1. Sjeng 11.2  . . . . . . . . . . . . . . . . . . . . . . . . . 0.885416(7)

  2. Olithink 2.2.1 [OliPow] note "A" . . . . . . . . 0.5625(0)

  3. Pulsar 2009-9b  . . . . . . . . . . . . . . . . . . . . . 0.411458(3)

  4. Gerbil 02 note "B"   . . . . . . . . . . . . . . . . . . 0.3541(6)

  5. KKF 2.6.6 . . . . . . . . . . . . . . . . . . . . . . . . . . 0.31708(3)

  6. Nebiyu 1.41 notes "C[.x]" . . . . . . . . . . . . . UNDEF. (0.275(0+), est.)

As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum (first & second contain the pertinent "Losers tournament"" tables, the third & fourth contain tables for "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).

  1. Sjeng 11.2  . . . . . . . . . . . . . . . . . . . . . . . . . 0.885416(7)

  2. Olithink 2.2.1 [OliPow] note "A" . . . . . . . . 0.5625(0)

  3. Pulsar 2009-9b  . . . . . . . . . . . . . . . . . . . . . 0.411458(3)

  4. Gerbil 02 note "B"   . . . . . . . . . . . . . . . . . . 0.3541(6)

  5. KKF 2.6.6 . . . . . . . . . . . . . . . . . . . . . . . . . . 0.31708(3)

  6. Nebiyu 1.41 notes "C[.x]" . . . . . . . . . . . . . UNDEF. (0.275(0), est.)

As to engines that play Losers Chess within a WinBoard environment, it seems that the answer is unfortunately no: Sjeng seems to be the strongest of these (within context), though at least OliThink seems likely to give you a greater challenge than you might from Pulsar.
     The results of several competitions (w/ environment data included) in Losers Chess (each with some changes in competing engines involved) are posted at the ImmortalChess forum (first & second contain the pertinent "Losers tournament" tables, the third & fourth contain tables for "Suicide chess tournament" from which to infer Nebiyu's possible strength by comparison).

  1. Sjeng 11.2  . . . . . . . . . . . . . . . . . . . . . . . . . 0.885416(7)

  2. Olithink 2.2.1 [OliPow] note "A" . . . . . . . . 0.5625(0)

  3. Pulsar 2009-9b  . . . . . . . . . . . . . . . . . . . . . 0.411458(3)

  4. Gerbil 02 note "B"   . . . . . . . . . . . . . . . . . . 0.3541(6)

  5. KKF 2.6.6 . . . . . . . . . . . . . . . . . . . . . . . . . . 0.31708(3)

  6. Nebiyu 1.41 notes "C[.x]" . . . . . . . . . . . . . UNDEF. (0.275(+), est.)

3 Removed first two items from list (further research indicates that they are inapplicable here); edited table to reflect new reelative strengths.
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2 Removed typo following decimal place in Sjeng's normalized average score.
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