The Atari OS appears to be a closed system meaning only programs available through their store ui can be installed. It's also a version of Debian Linux so debian programs shouldn't need porting at all. If you had access to the linux terminal you could install programs, even a linux desktop; no need to boot to an alternate os. There is suppose to be a software development kit you can download/install from atari. Maybe the sdk gives access to the linux terminal.
Arcade1up not withstanding, there isn't a lot of money in classic video games so you'll rarely see third party licenses, however the atari vault and flashback classics does have m-network games. I wouldn't expect to see any video game in any mainstream store that is not propely licensed.
The Antstream Arcade is an app storefront where you can buy games, most of which are retro-aesthetic and not actual retro games. This is different from the vault, where the pre-installed classic arcade games are found. This is more akin to Steam or the Google Play Store, with modern games available for purchase and download. I really enjoyed Unsung Warriors, a side-scroller with some tight controls and a cool cartoonish style, but you can play that on Steam. In fact, just play it on Steam.
With gift card in hand, game lovers just download the GameTap software, which acts as a gateway to the GameTap vault. The multi-level vault features a diverse mix of titles and platforms - something for everyone. These are organized in a series of game rings, including "hot picks" and user favorites, as well as games organized by game type (e.g., action, adventure, strategy, etc) and game system (e.g., Sega Dreamcast and Genesis, Atari 2600, PC games and more). Once a game is selected, each title displays an associated "InfoCard" that includes directions for playing, control options, and tips, as well as parental controls (the vault contains "E," "E10+" and "T" titles, only) and top scores from the GameTap community. 781b155fdc