Wow! What a unique vision for a simple concept. Does wonders for RPG'rs who have to use handfuls of dice for specific reasons.
For complex RPG dice sets this is the only program to look for, currently on the Mac (still looking for a super simple small-footprint program that handles the opposite end of the spectrum).
A few simple changes will make this a 5! A few simple feature additions will make it a SOLID 5. And being free, you can't really beat this anyway.
Here are a few suggestions for a minor upgrade:
1. If possible, find an easier way to set-up the hands/sets. Though impressive and functional, I was jumping around and clicking everywhere to set up sets. Dragging and dropping the dice images onto the "set" might be a more intuitive option (but maybe about as busy, though).
2. Color code the dice/die representations (at the top and in the set representation.
3. Add a D30, and possibly a custom "value" so a die (or dice) in a hand can be odd numbers, like 7, 21, 365, 400, or 1000, etc. Along with this, adding a sum to a die (+/- a certain value) can also be helpful... Die results that start at zero, negative to positive ranges, a true percentile representative (0-100), etc. Though not of much use in D20 systems, this was a constant need in a lot of older SF and miniature games.
4. For design and readability only... the totals (sums) should be just to the left of the "die" markers. It's tough to instanly see what is connected to what, if you have to scan across a possibly near-empty set.
5. This might be difficult, but many games have methods of skewing dice rolls by elininating one or more of the high or low rolls. If a hand can be "auto-sorted" (without moving the "dropped" switch) this can be done automatically using the "dropped die" feature. As it stands right now, the dropped function on a die follows it in the sort.
6. And, this is purely my own taste, but I hate the metal interface and actually find it difficult to "stare" at. If this is true of other users, you might want to allow changing the interface, or even desining one uniquely your own.
Once again, excellent job!