99 Spirits and
Tsukumogami are DRM-free.
I tested
Vanguard Princess again, but I couldn't get it work without Steam, so I'm removing it from the list for now. It could be that I had to install some dependencies, but there were no packages in the game folder. If anyone can get it running, that would be cool.
@cmdr_flashheart: I noticed that some games like 99 Spirits and War of the Human Tanks only work when the steam_api.dll is present in the game directory. When you delete it, the game gives you an error and is unplayable. It also doesn't matter if it's on the same PC or on a new machine which never saw Steam in it's life. So you maybe should paraphrase that steam_api.dll thingie.
Dolantin: Steam's Desktop Dungeons (windows) marked with a '?' in the wiki is DRM free.
Simply delete both .dlls
Could be of interest for people who don't know if they want to buy the actual 'humble' or wait for a steam sale.
The '?' in the wiki is a place holder because someone said somewhere that the game is DRM-free, but never mentioned for which platform. I
assume you are using Windows, like the majority of people, but that doesn't qualify for an exact entry.
edit: grammar & duplicate