Make RAM Disk is an application that provides an easy way to create, format, and mount a RAM disk in one shot.

What's a RAM disk?
Most disks (more accurately, volumes) are backed by some sort of permanent storage, such as an optical disc (as in CD and DVD), magnetic hard disk, or flash memory. In all of these cases, the data on the volume will persist after the computer is shut down, because it's been written to permanent storage. (Sometimes that isn't true, but it's very very rare.)

A RAM disk, on the other hand, has no permanent storage behind it. The data on the RAM “disk” is stored only in RAM (memory), and will be forgotten at shutdown.

Why would I want this?
A RAM disk is at least as fast as your hard drive, but temporary. You can use it as fast storage that won't interfere with hard drive I/O, and for anything you don't want to keep.

A RAM disk is great for screen-recording temporary files; if you use iShowU, see the Storage tab of its preferences. You can also put your Downloads folder (in Safari, Mail, Adium, etc.) on a RAM disk, since you won't always want to keep things you download.

Requirements:
OS X 10.4-10.6
Universal Binary