
There are two other ROMS I've come across, but both are recently developed, unlike FlexiDOS.
Fabrizio Di Vittorio has developed a diagnostic ROM (2019) to test the firmware of the TC01. The ROM checks the RAM, PSG (AY-3-8910) and connected keyboard, VDP (TMS9129) and VRAM, FDC (FD1770), CTC (timer), PCI (8251 USART), and PIO (parallel IO). This is available on GitHub.
Charlie Robson has developed the EinSDein SD card interface that is supported by an additional ROM. Further details of the einSDein are also available on GitHub.