Also Zoom Platform (unrelated to the videoconferencing program, AFAIK they even predate it): https://www.zoom-platform.com/

Its selection is small but it has a few exclusives - Alien Trilogy was released recently-ish there. Also they're the only place where you can find the original Duke Nukem 3D with all of its expansions due to some perpetual contracts they had with 3D Realms before the IP was acquired by Gearbox.