Mutant Future is a retro-clone of the old TSR Gamma World Game. There’s a commercially available printed version, but you can also download an artless version if you just want the rules.
Rules Design
Templates For Playing Cards
If you’re designing your own games, here’s a page with some pdf, ai and psd templates for playing cards of various sizes. I’ve taken to making unit cards rather than roster sheets for players to keep track of information in my games.
Creating Data Driven Graphics In Photoshop
This tutorial would be useful for generating large sets of gaming cards.
Dice Probability Calculator
Anydice is an online probability calculator. Useful for game and rules designers.
Probabilities of Odd Dice Combinations
Gnome Stew has an interesting article on the probabilities of various polyhedral dice.