I take a screenshot every 3 minutes, so when I come to do my timesheets I have a pretty accurate idea of what I was doing.

If anyone would like a way to do that on OS X, get in touch.

Although the way I do it relies on Emacs, a suitable Emacs is included in all recent versions of OS X, and I can provide instructions that require no knowledge of Emacs.

However, you will need to run a command from the "command line" (from Terminal.app that is) every time you restart your Mac since I have not mastered the part of OS X (namely, "launchd") that would allow me to instruct you on how to have Emacs and my code start automatically on restart and I have not mastered the parts of OS X that would allow me to create a proper app (as opposed to a "command line").

Still, if you do not mind mucking with Terminal.app, my solution is fairly robust. For example, you do not have to use Terminal.app every time your computer wakes from sleep because my code survives the Mac's sleeping and waking. (For the Mac to sleep when you are away from it is helpful because then you do not have to review a monotonous series screen shots of when you were away from the Mac.)

Is there any software you would recommend for this?

My own research points to AutoScreenShot.