[userbinator]

DivX/XviD yes, but not H.263. Patents for H.263 expired long ago. This is MPEG-4 ASP, which is a superset of H.263.

(Source: have written a H.263 decoder as a learning exercise.)

[anthk]

H.263 was used as the former codec of Netmeeting (and maybe some other VoIP software too).

[userbinator]

H.263 was definitely a standard in videoconferencing and low-bitrate video in general (YouTube and many other streaming sutes used FLV1, which was a variant of H.263) prior to H.264.