mock and mach: building Linux programs for other distributions

Mock and mach are both ways of building Linux programs for other distributions. So why do you care? Simple: they're the easiest way of building x86 binaries on an x86_64 system.

(You would think that 'cross' compiling would be the easiest way, since it's just building for a different ABI. Tragically, it's not, at least not in Fedora Core 5.)

Both work by installing a complete (although usually minimal) copy of the distribution you want to work in and chroot()'ing into it to do work. Mock is very specific to building RPMs in a guaranteed clean environment; mach is more general, and so is useful for building arbitrary programs from source. Both are part of Fedora Extras.