Games for the Dreamcast that were produced without the permission or knowledge of Sega.
While the Dreamcast used a proprietary disc format (GD-ROM) which made piracy and unlicensed publishing very difficult, the combination of the discovery of an exploit in the also supported MIL-CD format which allowed the execution of unauthorized code, the development of an independent software library (LibDream, now KallistiOS), and the leaking of the Windows CE development kit enabled homebrewers and bootleggers to write and publish their own software.
Following the Dreamcast's discontinuation in March 2001, it has since become one of the most notable platforms for homebrew development.