XviD aims to develope a high quality open-source MPEG-4 codec. As you may already know, XviD comes from the same open-source project that was the basis for DivX 4.x/5.x, but instead of going all commercial, XviD remains open-source.
Seeing that XviD official website is down, I decided to link to Koepi's 1.0 build
which I have been hearing is more stable and reliable.
Download: XviD 1.0 codec