Apprentice makes designing and running your Dungeons & Dragons 4th Edition encounters simple. It replaces monster cards, character sheets, and other scraps of paper with an easy-to-use interface that puts all of the necessary stats at your fingertips.
You simply populate your personal database with creatures and player characters, then design encounters with the appropriate mix of combatants. When you're ready to run your encounter, you'll have everything you need right on one screen.
Best of all, Apprentice is browser-based, so it's cross-platform and Mac OS friendly, and doesn't require you to download or install anything. (An iPad interface is also in the works; check the feature roadmap for details.)