Only if the developer uses the Steamworks API. If you purchase a game on Steam that does not use any Steamworks, once it's downloaded, you can run it from your

Only if the developer uses the Steamworks API. If you purchase a game on Steam that does not use any Steamworks, once it's downloaded, you can run it from your computer without Steam running. Many old games you can buy on steam are just the original game with a DosBox launcher that just sits in your SteamApps folder unprotected.