Optimal

The only dice roller you will ever need. I cant think of a way to compute a die roll that this app cant perform, it allows for quick access to regularly used rolls, provides complete breakdowns of all rolls made, saves history, and will even graph any roll you produce to give you an overall idea of the probability curve.
Its not necessarily pretty, and its not necessarily simple to use, but the sheer power and utility of it completely overrides any criticism I can imagine.
Incidentally, the nearby review from "Daemon-" is either misinformed or outdated, because the program is amply equipped for Storytelling dice pools.

Obscure42 about RPG Roller, v2.2.2