Sign up to the 60th anniversary celebrations and claim a free Steam copy of the SEGA Saturn cult classic NiGHTS into Dreams when you link your Steam account (while codes last).
Once you sign up and link your Stream account, you get the following message;
NiGHTS into Dreams has been successfully added you your Steam Inventory. Check your Steam Library to download & enjoy the game.
Checked my steam library and it was there straight away.
Credit: r/GameDeals
This still works except for some reason it broke on 2 different accounts with different browsers (although both Firefox based). The first time I connected my Steam account it went back to Sega and after connecting or something it lead me to a 404. I went back and tried again with same email and account, and the second time it was fine and added it. Same thing on both accounts, so seems more like a bug than a random error.