A major selling points is their distribution of games without DRM, in contrast to services such as Steam and Origin. Additionally, the older games in their catalog are all modified to run properly on modern systems, sometimes better than they did at the time (frequently using DOSBox and ScummVM emulation), and usually include lots of feelies such as soundtracks, manuals, and forum avatars, as well as scans of feelies which came with the original game (maps, comics, and the like). With older games, the feelies frequently take up more hard drive space than the game itself.
Many of the titles in their catalog are compilation re-releases: for instance, the first three Ultima games are one package, the next three are another, Ultima VII and its Expansion Pack Serpent Isle are a third, and the Ultima Underworld duology are yet a fourth.
Since August 2014, GOG.com sells DRM-free movies, so far mostly indie productions which touch upon the gamer and nerd culture in some way.
In 2016, GOG.com launched a completely optional (aside from multiplayer) standalone client similar to Steam and EA's Origin called GOG Galaxy and began doing big sale events similar to Steam's.