XChat? Open-source? Sorta. The Windows version is just like mIRC, and the linked 'homepage' is not the official one (now changed to real homepage). One can compile XChat yourself (there's a tute on the silverex page), but it'll be using the *nix source, rather than the Windows source that the official Windows release is compiled from - and thus will be a little buggy.
I see where you're coming from. Thanks for the update, I made the section. --Calvin 01:49, 15 October 2008 (UTC)