Is this anything like the game 'Warchon'? Cause I've had that on my wishlist trying to figure out how it works. https://boardgamegeek.com/boardgame/4508/warchon
I'm afraid I know nothing about Warchon. Backbone also isn't a game (although it contains 3 sample games). An SRD is a "system reference document" you can use to create your own games. In this case, bookmark games–games that live on a bookmark and are generally intended to be played paired with a book of your choosing.
Plus, it's free, so no harm in you checking it out!