When I first wrote this program back in 2005 or so (yes, it's been that long), I was a poor, starving graduate student hacking away in a small apartment. In some sense this program taught me how to write Java which of all things opening up some interesting career opportunities. At the time many very kind souls offered to throw some change my way for writing and supporting the software.
The good news is that (1) I graduated and (2) I'm no longer starving.
All that said, if you still want to donate $10-$20 or whatever to the support effort, I will not refuse it. Just understand it might go to baby food or diapers. Priorities change, you know.
RainScatter is and will remain free to use and even improve (you have the source code, too.) If you still insist on making a small donation, you can make a contribution via paypal to aflowers at frontiernet.net, or to my callbook address.