The Steam version has no DRM. The executable will run without Steam.
Steam doesn't have any default DRM, but a lot of games don't have a fallback if the Steam integration doesn't find Steam at startup and often just crash silently. (Often this can be fixed by adding a steam_appid.txt file in the same folder.)
The Crimson Diamond doesn't have that problem, though. It will run fine as-is.
Viewing post in The Crimson Diamond FULL GAME comments
Thanks Rainwarrior. That was my main concern (and why I don't like to buy on Steam as a rule; I definitely consider "must always be running Steam" as DRM!). I would still prefer GOG so will wait a bit for a release there hopefully, but it is good to know that Steam copies a) aren't DRM'ed and b) will survive after download even if Steam ever shuts down. :)