Synergy+ lets you easily share a single mouse and keyboard between multiple computers with different operating systems without special hardware. Synergy+ is an actively maintained fork of Synergy/Synergy2.
iMouseTrick is a program that clicks the mouse for you as many times and as fast as you want. This program could be useful when you are playing a game where you need to do a lot of clicking and you're not fast enough or you don't want wear your finger out.
BtBatStat is a simple OS X app that shows the battery status of your Apple bluetooth mouse and keyboard in the menu bar. It supports the Apple BT keyboard, Apple Mighty Mouse, Apple Magic Mouse, and the Apple Magic Trackpad.