Are you a "CrackFlasher"?! Good me too! Boot Manager is for you. It gives you the ability to run up to 5 custom roms on one phone all at the same time. It is super easy to use and flash from one rom to the other. I like to use this to test roms that are not completely stable, like beta roms, and alpha builds, but you can use this to flash a rom that maybe you have never tried and still keep your main phone rom the same. The way the app works is it copies an image of your current rom and saves that, then you install any custom rom to one of 5 slots it creates on your sdcard. You can then boot into one of your "sdcard" roms, and use it the way you would any other rom. You dont loose any functionality or stability or speed when running the rom from your sdcard infact you probably wont notice a difference at all. Once you have finished playing with your "sdcard rom" you just boot back into your "phone rom" its as simple as that.
It is supported on multiple devices and the list is long Htc Desire, Evo, Evo3d, Incredible, Thunderbolt, Inspire, Sensation , Droid, Droid 2, Droid X and more!
On DroidX and other 2ndInit devices your phone rom must be a second init rom that is on the GB kernel.
Also when installing an sdcard slot rom be sure to go into settings/display settings, and put the timeout at 30 minutes, if the screen turns off during a rom install it wont turn back on. You will have to pull the battery and reboot the phone to turn it back on.
Grab the App here : https://market.android.com/details?id=com.drx2.bootmanager&feature=search_res ult
You can find support for the rom : Init 2 Winit Forum • Index page
Also you can email their support team Support@init2winitapps.com