Some sort of “system program” that features a hex editor, disassembler, port monitor, etc. akin to KnightOS’ features.

https://www.ticalc.org/archives/files/fileinfo/196/19619.html

the pieces of KnightOS are maintained as separate projects under the KnightOS organization

Compatible with the TI-73. The most recent versions may support USB upload from PC, allowing this to effectively completely replace the original calculator OS.

https://knightos.org/

https://github.com/KnightOS/KnightOS (git most recent & USB, but compile difficult)

https://www.ticalc.org/archives/files/fileinfo/463/46387.html (precompiled, NO USB!!)

The only ASM shell for the TI-73 w/ dedicated programs, unless you want to count Swan or KnightOS. Has two versions, 0.2 and 0.3, with 0.3 apparently being just a test.

https://www.ticalc.org/archives/files/fileinfo/366/36618.html (0.2, for TI-OS 1.6)

https://www.ticalc.org/archives/files/fileinfo/388/38805.html (0.3, for all TI-OSes?)

A flash shell that can run Mallard programs. Little information about appearances.

https://www.ticalc.org/archives/files/fileinfo/455/45516.html

What even is this? The TI-81 has no way to communicate with a PC.

https://www.ticalc.org/archives/files/fileinfo/48/4859.html