GOG.com

Sad thing that so many people still stick to Steam/Origin/etc, when there's such a great alternative available. The main strong point of GoG is that all games they sell lack any kind of DRM systems implemented, which is a cancer and often a violation of user's privacy in almost any other digital distribution platform today. This is something diametrically opposite, though - every GoG game works without any internet connection, nor client required, just like majority of pre-2005 physically-sold titles would (there's optional downloadable client, called GoG Galaxy for those who like such things, but i haven't tested it). You can redownload everything you have purchased as many times as you like, and even if the shop goes out of bussines at some point in future (which i REALLY hope won't be the case anytime soon) all the installers you keep locally will remain fully usable, just like physical copies back in the day. Moreover, there's no legal limit in the number of physical workstations you are allowed to install your games on, according to the official website:

Can I enjoy my purchases both on my laptop and desktop computer at home? Yes. We do not limit the number of installations or reinstallations, as long as you install your purchased games on computers in your household. So yeah, if you've got a render-farm in the basement, you might actually break the world record for the number of legal Witcher installations in one household. However, if you think about installing your game on a friend's machine or sharing it with others then please don't do it, okay?

The only thing some people may complain about is the fact, that despite numerous newly released titles are available on GoG, there will always be many AAA games that you won't be able to buy there, since some publishers won't agree to strip the games off DRMs. I personally don't care, and deliberately boycott Steam and others. If majority of people did the same DRM stores would have gone extinct sooner or later, i believe.

No longer DRM-free: https://www.gog.com/forum/general/drm_on_gog_list_of_singleplayer_games_with_drm/page1