As I said earlier, this HOWTO doesn't cover the Series 3 ( e.g. 3/3a/3c/3mx/Sienna ), however, as I run into information, I will try to place it here anyway. This section will probably never be organized (unless someone else keeps it uptodate), but it still might contain useful information.
nfsc is a VT100 emulator from Rudolf König.
Nick Murray has created Shell3a, which is a command line interpreter which allows basic file operations as well as some sophisticated functions such as command history, filename expansion, batch file support, input and output redirection, pipe like feature :), aliases and shell variables, keyboard remapping and macros and UNIX or DOS syntax for pathnames.
PsiLin, mentioned in the Series 5* sections, also supports Series 3*
Various utilities for Series 3* from arb.
Zerlegeanleitung Psion Serie 3a, e.g. Disassembling a Series 3a (in German only)