I am interested because it is barely impossible
PS: Yeah,this way you can't get a game on steam for free because you obviously have to buy it ( there were some work arounds for some games like Borderlands 1 to get it for free by tricking steam that you want to transfer gog version of the game into your steam acc, but this method doesn't work anymore.) So basically this is just a cracked game, (which I don't recommend downloading it from those sites) which uses Steamworks fix which is something like p2p emulator that allows multiplayer with all people that have the same fix (the same cracked game with this fix) and by also using emulator like SSE that allows you to run the game without steam and/or without cracked executable. And CreamAPi is another very great tool that allows you to unlock DLC for cracked games, or even if you have legit game on steam.
For those who just wonder what is this,It isn't anything special. you cant get your game in your steam library, but with this method you can play multiplayer with the same user for steamwork fixs, which is nice if you want to play with friends.