QL

Here is a visual compilation of the Old Machinery blog posts about the Sinclair QL computer and some pointers to replacements.

1. Display: RGB TTL, RGB Scart, Composite Video, TV. Connecting to 1084S.
2. RWAP Keyboard membrane replacement
3. Extension slot: Tetroid Disk Interface or Gold Card (QubIDE interface, Memory/CPU expansions, Super Gold Card)
4. HxC Floppy Emulator, connected to the TDI / Gold Card. Image format.
5. QL-SD Microdrive replacement
6. Minerva ROM upgrade, alongside the QL-SD
7. EPROM Cartridge -  e.g. Toolkit II ROM
8. Serial cable and PC file transfer
9. Network cable for linking two or more QL computers

Here's a table of some of the more notable modern peripherals and their features :

                      TDI      GC       SGC       QL-SD
Card Reader:          YES(CF)  NO       NO        YES(SD)
68000/Acceleration:   NO       YES      020       NO
Memory:               800K     2MB      4MB       NO *)
Disk interface:       YES      YES      YES       NO
Battery-backed clock: NO       YES      YES       NO
Toolkit 2:            YES      YES      YES       NO
Minerva ROM:          NO       NO       NO        YES

*) The file allocation table requires memory

TDI = Tetroid Disk Interface
GC  = Tetroid Gold Card Clone
SGC = Tetroid Super Gold Card Clone
Ql  = SD=SD Card reader