If you're a flashaholic on your HTC EVO, chances are you've run into that horrible moment when you realized you left something two or three ROMs back that is no longer available. The general solution is to re-download it and move on with your life, but what do you do when that old app you want is no longer downloadable anywhere but you have it backed up on an old Nandroid? Or perhaps you realized you lost an important text message or contact and didn't notice it for weeks.
The old method to recover a single piece of data or apps from a Nandroid was to make a backup of your current setup, restore the old backup with whatever you wanted on it, export your text messages or data (using an apk grabber), restore the last backup you made, and then import the data/install the apps you needed. Whew!
A neat little program called AppExtractor by AppsByAndy can extract individual items from your ClockworkMod Nandroid backups, allowing you to do in a minute or two with a couple of taps what used to be a really labor- and battery-intensive effort.
The app currently only works with ClockworkMod/ROM Manager backups, as mentioned at the top of this post, but hopefully will be expanded to include Amon Ra (same basic structure as CWM) and TWRP (which will require some effort due to data compression and win).
Even if you use a non-supported recovery/backup, this is still something to watch. Some day it may save you a lot of headaches and time.
As with every root app, I suggest you make yet another Nandroid before playing with this. No developer alive can test every ROM with every possible configuration of phone, partition setup, app environment, system tweaks, third-party software, and so on. In trying to recover your text messages from ROM A to ROM F, you might end up with no texts and an unworkable phone, so a Nandroid can be a lifesaver.