Control Program/Monitor - CP/M
CP/M is a very basic disk operating system developed by Digital Research that predates Microsoft MS-DOS and was available for the Intel 8080 CPU with which the Zilog Z80 is fully compatible. Timex of Portugal paid 400.000$ (about 2000 Euros) for the license and by that time it was a lot of money.
Professional software would not be necessary to be recompiled so a lot of software would be readily available with very minor changes.
Since the Timex FDD3000 can boot any OS, Timex wrote the BIOS for FDD3000, made the Terminal Emulator program so users can use CP/M with a normal Timex Computer/ZX Spectrum, and developed the Timex Terminal 3000 (TT3000) keyboard to use CP/M directly on the FDD3000. The Timex Computer 3256 would also be able to be used as a CP/M terminal keyboard just like TT3000.
Those screenshots show the Terminal Emulator program waiting for the CP/M to be booted on the FDD3000.