I've made a portable version of TTCalc, which is a multi function Calculator with a nice interface. The portable version creates it's regular settings under C:\Documents and Settings\[CURRENT USER]\Applications Data\TTCalc, it will back up the original if there is one. When closed the portable settings will be copied to its folder and the local backup put back. If you have no local install, it will delete the folder completely. On the next run, it will use the settings on the deivce which remebers things like the position of the calculator on the screen, and whether or not it was collapsed, etc.
And for anyone who wants to see that it's actually a pretty nice calculator with good functions, here's some Screenshots