Dear Esther is sold DRM free on the Humble Store. That would suggest that DRM free source games are possible. I can't say anything on the Steam version of this game, however.

Therefore this claim might also be only partially true.

(Yeah, b****h, I taking you apart one by one ;-P)

I think Bloodlines and Black Mesa will also support your claim, ain't both of those Source Games?

Nope. Dear Esther definitely needs the client to run. I just tried it. It doesn't start the client, though. It simply gives you a message asking you to kindly run Steam before running Dear Esther.

Just tested a few more another shorter list which started the client :

Beat Hazard
Vampire : Bloodlines
Crysis Warhead
GTA Vice City
Tropico 4

Black Mesa requires Source SDK Base 2007 to run which can only run under the Steam client. When alt tabbing out it shows as SDK Base running not Black Mesa, there also isn't an exe file for Black Mesa source looking in my Source Mods directory and sub directories.

OK OK, fookin hell, I got something wrong, I am trying to help out here, its now getting shoved in my face for a daft mistake. Bolocks to it, why bother :(

If you want to be 100% sure a game is really DRM-free the only sure test is :

Copy the game folder to another offline computer, partition, VM, whatever, on which Steam was never installed and try to start the game there. If it start and runs Ok then the game is DRM-free.

I have some game that worked fine "without" Steam started, but refused to start on without Steam installed and/or without the local user registration information (the stuff that allows you to run Steam in offline mode). Also you have games with third partied DRM that might accept to run without Steam but are far from DRM-free.

I hope you understood that I was just jesting you, right? You did some awesome legwork for us!

Seeing as it was you yeah, just seems you mentioned it and so did Basilisk (simultaneously) but then seem to be getting others piping in pulling me apart.

I use Steam a fair bit and have over 100 games installed currently, so thought what better way to help out a great thread and hopefully to enlighten a few users at the same time.

Don't take it the wrong way, you're being a great help.
You have a point there, but that would be rather time-consuming. We could make that round two of the testing. For now, I think this will do.

You can add to the DRM-free list:
Faerie solitaire
Machinarium

Nice work!

I won't actually use this myself because I enjoy using the steam client (gasp!) and I regularly use offline mode without problems, but plenty of people will find this useful. Thanks for your effort.

Good stuff :) +1 from me.

I'll have a gander to see what I have installed under Steam later to see if any of it runs DRM free.

There are also some DRM-free games that if you just copy the files from one computer to another will not work and require to be installed, Baldur's Gate 2 for example. I usually look at games that can be copied from one computer to another and still work as portable games, or ones I can put on my portable drive and play on any computer. I wonder if those games would work if you uninstalled steam on the machine they were originally installed on. Thats probably way to much work though.

Great list by the way. I always wanted to make something like this but for D2D or Gamersgate games.

Yeah, that's a good point regarding the terminology. We're actually looking for "portable" games here, because Steam doesn't provide an installer (let alone a DRM-free one) like for example GOG does.

I'm reasonably sure these games would run even after you uninstall Steam, but if they for example rely on something being written to registry during the first launch, they won't be movable to another computer unless you create the same registry keys there. Which still is possible, but it would quickly become a huge pain in the arse.

Confirmed:

Ben there, Dan That
Blackwell series (all games, achievements disabled)
Bob came in pieces
Breath of Death VII
Containment
Crayon Physic Deluxe
Cthulhu saves the world
Data Jammers Fastforward
Defcon
Dungeon Siege 2 (but not 1 or 3)
Eufloria
Faerie Solitaire
Frozen Synapse
Gratuitous Space Battles
Jamestown
Lightfish
Lone Survivor
Lunar Flight (Do all unity games work without steam? same as DOSBox)
Mini Ninjas
Multiwinia
Noitu love 2: Devolution
Pixeljunk Eden (error message can be dismissed)
Psychonauts (Wheeeeeeeeeeeeeeeeeeeeeee)
Really Big Sky
Saira
SOL: Exodus
Spectromancer
Stranger's Wrath HD
The Path
Unstoppable Gorg
Vertex Dispenser