I'm using a todo tracker that I wrote last year in about two dozen lines
of shell scripts. It's not yet totally synced up to everything that it
needs to be for a full GTD workflow, but it has been a very useful capture
tool when the what to do next ideas happen faster than there is time to do them.

I've been using vi as my primary text editor for about a week and
relearning its charms. A bunch of writing has gone under source
control (using RCS for lack of any better idea) which is helping
checkpoint good ideas in progress. It's fun to write with a big font
and no interruptions.