The talk is almost exclusive about AMD and Intel today. But there are alternatives. PPC or PowerPC was earlier only something that Macintosh used, but now there are starting to appear other platforms based on the same type of processor. One company which has come a long way in the development of mainboards is Genesi, with its Pegasos board. This is the second generation’s PPC system. So far it is ”only” available with a 1GHZ G4 CPU at most, but we will probably se dual processor configurations with the G5’s CPU within a near future.
The operating systems that work on the PPC platform is mainly MorphOS, but several Linux distributions are being ported as we speak. One of the larger Linux dists for PPC is YellowDog, but Debian and a number of others has released own versions.
Read more on the manufacturer’s homepage here.
Edit: There is of course also the AmigaOne, for you who want to have the best computer of them all ;). More information can be found here.