Sega Ages refers to a number of compilations or re-releases of classic video games from developer and publisher Sega. Two versions were released only in Japan: the first for the Sega Saturn while the second for PlayStation 2 (the latter known as "Sega Ages 2500"), which included 3D graphics and new gameplay features. In America and Europe, some 2500's games were released for PlayStation 2 as part of Sega Classics Collection. Finally, there is also the Sega Ages Online series on the PlayStation Store for PlayStation 3 in Japan.
The Sega Ages series differs from most "retro" video game releases in that rather than compiling a number of games, most of them contain only one game and are instead sold at a very low price.
Sega released several Sega Ages games for the Sega Saturn in Japan:
These versions of Space Harrier, Out Run, and After Burner II were released in North America and Europe on a single disc called Sega Ages.
Sega Ages 2500 is a series of budget-priced games published by Sega, released for the PlayStation 2 console in Japan, with each game sold individually. Initially, these were part of a joint venture with D3 Publisher called "3D AGES" (SEGA D3 spelled backwards). These releases were primarily remakes of classic arcade titles with modern 3D graphics and new gameplay features, but also included 2D remakes (the Phantasy Star games) and ports (Virtua Racing and Bonanza Bros.).
Sega assumed control of the project with the release of Decathlete, and the 3D AGES development studio was retired with the release of Phantasy Star Generation 2. At this point, the direction of the series shifted focus from remakes to compilations of emulated titles, and ports (enhanced or otherwise) of classic Sega games. Sega produced these titles themselves, but the actual development work was frequently outsourced to other studios, most notably M2.