The are hundreds of incredible references online dealing with the history of computing, and especially about the TI-99/4 and TI-99/4A computers. I list as many as I can find for your reference:
- Centre for Computing History = This is a UK-based, general computing history website that has numerous articles involving the TI-99/4A.
- Eli's Software Encyclopedia = This software focused website includes many articles about TI-99/4A software. It's written using MediaWiki (the same software as this website and Wikipedia).
- Mainbyte = A retrogaming website including information about the TS 1000, TI-99/4A, TRS 80 PC-4, and the VIC-20.
- Moby Games = A general video game website that hosts several TI-99/4A game pages.
- Ninerpedia = A great resource run on Mediawiki (the same software as Wikipedia and this website).
- Rediware's TI-99/4A Page = Rediware has information about software and other items, including a fairly extensive set of TI-99/4A pages. I link to Rediware's main TI-99/4As landing page.
- Retrogaming Times Monthly = An archive of an older website covering multiple 1980's computing devices.
- TI-99/4A Videogame House = A strictly TI-99/4A page covering many of the most popular video games for the TI-99/4A. One of my favorite resources. It hasn't been updated for a while, but neither has the TI-99/4A, so it's totally legit.