Okay, I've updated the list with all the new comments here. Thanks again, guys! I also added Sonic Adventure DX, which needs Steam.exe to be renamed in order for it to not start the client.
viico: (full disclosure: I'm one of the developer and I'm outrageously posting it here)
BOMB is the aerial-combat game you get when you mix Crimson Skies and Porco Rosso.
store.steampowered.com/app/301500
No DRM whatsoever, you can copy the game's folder and put it right away on your USB stick or BitTorrent!
One limitation though: no server browser outside of Steam, just direct IP connections.
edit: sorry, can't post URLs
at the moment...
Holy crap, I love people like you. I need to buy your game just to support you guys for being so cool! Is it both the Windows and Linux versions that are DRM-free? Thanks again for the info!