For those wanting to write their own software, TiVo provide downloads for TiVo Beacon SDK (723k, zip) , TiVo Desktop Plug-in SDK (482k, zip) , Example Apache plug-in for Music and Photos v1.1 (12k, Source code) , TiVo Home Media Feature: Music and Photos Server Protocol Specification v1.1.0 (PDF), TiVo Connect Automatic Machine Discovery Protocol Specification v1.5.1 (PDF).
TiVo also provide open source "HME software" for broadband TiVo applications. There is a SDK, UI Toolkit for TiVo-style menus, Developer's Guide and UI Documentation.
There are numerous independent open source projects and books on hacking the TiVo. Andrew Tridgell gets frequent mentions in these for his work in Australia on interfacing the TiVo (he got it to work in Australia years before the official introduction):
"... However, this capability was denied the rest of us until a pioneering effort by Andrew Tridgell (Tridge) developed the original network adapter for the TiVos that enabled people to use certain types of older PC-style ISA ..." (Hacking the TiVo, on Page 87).