Computer Role-Playing Game
Adam Haase has been currently crafting a CRPG (Computer Role-Playing Game) using the original TI-99/4a hardware. He is using a special piece of hardware that has a PIO port and uses a CF card which not only acts as a disk drive, but also a 32k memory expansion and replaces the connection to the Peripheral Expansion Box.
Adam's current blog regarding the progress on his CRPG can be found here: http://www.adamantyr.com/crpg/
Assembler for 990 Mini Computer
While not a 99/4a developer, Dave Pitts worked as an Engineer for Texas Instruments, developing the operating system and assembler for the 990 Mini-Computer.
His assembler runs on the PC and is excellent for assembling (using the "-m 4" option) 99/4a assembler code. The resulting output is a text file (which would be DV/80 on the TI) containing the tagged object code that can be loaded using Editor/Assembler Option #3.
The output file, however, can be copied into a "\DSK1" folder that can be easily read by Classic99 without conversion.
Fred has written an excellent utility named TiDir that allows people to create V9T9 formatted disk images and copy files between PC99 and V9T9 formatted disks to new ones. You can also view a TI disk directory, DV80 files and TI Artist images. You can also extract files and copy them to a PC folder.
I also believe that he is responsible for the Ti994W Emulator. It can be found on the Emulators page.
Rumor has it, there is a version which can take PC files and convert them into a 99/4a format for use on a disk image with most popular emulators.
Pitfall! is a jump & run game released by Activision for popular 80's game consoles like Atari 2600 and Colecovision.
From 2008 until 2010 a version for the TI-99/4A was written by retroclouds. It got released as both disk version and a 32K bank-switched ROM command module.
The source code and binaries were released in 2010. You can get it here.
A limited run of cartridges was made available in 2010. These were based on the popular Jon Guidry boards. The cartridge came with a label and sported a 32K (4x8) bank-switched ROM. This version can even run on the unexpanded TI-99/4A.
spectra2 is a library in TMS9900 assembly language for writing arcade games running on an unexpanded TI-99/4A console. The library will support sprites, speech & sound.
The documentation wiki pages can be found here.
Check the development thread for discussing future enhancements.