Cave Surveying Software

See the Survex website.

Information Retrieval Software

I actually sometimes get paid to write Xapian, which is nice. You can download it for free from the Xapian project website.

Software for RISC OS machines

I wrote a number of utilities for Acorn machines:

slrn

I've contributed a number of patches to Slrn in my spare time (the largest piece of work was the local spool backend). John Davis has folded most of these into the main source - here are the ones which hadn't been last time I checked: