Is there any a free software or free pgn files that presents a survey of all openings and their variations (the deeper the best) similar to those found in chess opening references like MCO or ECO ? I just want to explore and analyze the resulting moves and positions by myself. I am not asking for games but rather just openings and their variations in a software version instead of normal books.
I think you are looking for my Encyclopaedia of Chess Opening iOS app.
This app provides you the ECO openings, annoated games for each opening and lots of variation. There is an engine embedded for you to explore lines and positions.
However, this is not a free app but it costs less than a McDonald BigMac. Please consider if you are interested.
What do you call an opening? ECO would not be very deep, only a couple of moves usually.
On the other hand, if you get really deep, the number of variations will increase dramatically and you won't have time to study each and every variant down to move 20 or so.
I'd suggest to find out what kind of opening s you like (closed/positional, open/tactical, popular, off-beat, ...) and thereby limit your choices. Use a regular database and study how grandmasters handle the opening of your choice.