From what I understand, this is a DropMyRights alternative made by the makers of Spybot, Safer Networking.
http://forums.spybot.info/showthread.php?t=26555
I would say that it different in some way to DMR in that there lists of supported browser/email clients/IMs, etc. where there is no such differentiation in DMR, you chose the application you want to run with restricted rights and create a shortcut to run it via DMR, job done.
If I’m going to run an application with restricted rights I have to say I would much prefer it to be one by MS as they ‘should’ be able to get it integrated with the OS that they also built.
However, whilst Alter Ego may differ in whatever way (I don’t know exactly what that is) it is available and DMR has been dropped by MS with the release of Vista with its UAC, effectively abandoning this XP users to their fate. Perhaps in the misguided hope they will upgrade to Vista for better security.
Fortunately Bob and his useful software archive rides to the rescue of those wishing to use DMR. Check Bob’s, setup instructions and importantly the dropmyrights.msi file needed as MS have now cleared the original link.
You’ll find it here:
http://mysharedfiles.no-ip.org/DropMyRights/DropMyRightsInstructions.html 
Oops, thanks Bob, I forgot to post the link ;D