Hunter Davis has open sourced QuickGrapher
Hunter Davis, no relation (AFAWK) has made QuickGrapher, an HTML5 Equation Solver & Grapher Open Source. He's placed the source on github and in less than a week someone has ported it to Android. I messed around with the beta about a year ago and was really impressed.
Hunter has also Open Sourced another of his projects as well. Source Tree Visualizer which basically turns your source code tree into a real tree in a pretty landscape 
You can find Hunter's post about QuickGrapher here
and his post on SOurce Tree Visualizer here
Even if these two things don't appeal to you Hunter's blog is always a pretty good read.
Hunter Davis is an android coding dervish
Hunter Davis is on a 30 apps in 30 days kick at the moment and although I only have one android device (an unrooted nookcolor) and can't actually try them they do look like pretty good little apps and possibly quite useful for some. If you have an android device you might like to give them a try
http://hunterdavis.com/archives/category/programs/android-apps