MacV9T9 - A TI99 Emulator for the Macintosh, by Raphaƫl Nabet. - http://pytheas.club.fr/english/TI99.html
The Tutti Emulator - TUTor Tiny Implementation - an emulator of Tomy Tutor for Commodore 64 and disk drive. - http://www.floodgap.com/retrobits/tomy/emu.html
TI-99/SIM - An open source emulator for Linux/Unix and Windows. - http://www.mrousseau.org/programs/ti99sim/
PC99 Menu - Shareware front end for PC99. Allows you to easily change modules and disks. - http://www.btinternet.com/~shawweb/stephen/TI.htm
CaDD Electronics Home Page - Authors of PC99, a TI-99/4A emulator for the PC. Description as well as program, manulal and command module order information, - http://pw2.netcom.com/~mjmw/index.html