TI99Sim is a very good emulator of Texas Instruments TI99 home
computer running on Windows and Unix.
The emulator faithfully imitates the TI99/4 model
(see http://www.mrousseau.org/programs/ti99sim/)
PSPTI99 is a port on PSP of the version 0.1.0 of TI99Sim.
How to use it ? Everything is in the README.txt file.
Sources are included, and this package is under the GNU public licence,
read COPYING.txt file for more information about it.