So, I looked into NewOS, the kernel that Haiku is based off of. It hasn't been updated in 10 years (I gather that Haiku's fork has taken most of the attention, so that's neither here or there). That said, I found this amusing:
> The system currently can be built to run on the follwing systems:
> Intel IA-32 (x86) - Tested on desktops through 4-way servers
> Sega Dreamcast - Hitachi SH-4
> PPC based machines - G3/G4 Macs, Pegasos
It's still supported by OpenBSD and QNX as well. It's actually not really dead and is moderately popular in embedded systems. Also, the patents are expiring and the http://j-core.org/ project is working on an open-source reimplementation (they've already done SH-2).
Almost everything is still supported by mainline GCC. I don't know, it's a weird choice to me, given that BeOS never AFAICT supported Dreamcast either.
The Dreamcast has a pretty big homebrew scene because it was super trivial to run your own code on an unmodded console and it also ran some form of Windows CE. It was probably low-hanging fruit to add it and someone thought it'd be cool, though actually doing testing on the DC will give you a good idea of how much your changes are affecting the performance and resource utilization.
> The system currently can be built to run on the follwing systems: > Intel IA-32 (x86) - Tested on desktops through 4-way servers > Sega Dreamcast - Hitachi SH-4 > PPC based machines - G3/G4 Macs, Pegasos
Sega Dreamcast!