I've also just finished a tool that I've just got feature-complete: a GM Control Sheet. There are (probably always be) bugs, but now that the features are all in, I can squish in any of 'em we find.
http://jdgwf.github.io/gurps-web-tools/
Feel free to fork or contribute:
https://github.com/jdgwf/gurps-web-tools
Like haplessthrall, it's an HTML5 web app using localStorage and can be ran from your local machine. I'm targeting iPad sized devices for minimum usage -- too many fields to easily be used on a phone sized device.