Years ago I had a program for my Amiga computer that generated ambient "music". I Can't remember the name of the program.
You would input some midi notes from your keyboard, press play, and it would play these notes back (through midi) in random order/duration/timing/whatever  and  loop the entire mess.
Multiple tracks could be created and if you were lucky you would get great, dissonant, ambient "music".
It was fun to play around with once in a while. 
 
Does anyone know of a similar program that exists now?
Prefer Free.
Thanks.

I know it's not exactly what you're looking for but if you have Reaktor there is a great ensemble called Acoustring in the User Library which actually has a pretty decent little random note generator that you can tweak endlessly. Produces some really nice music.

Cool. Thanks, Sharke. I will have Reaktor shortly when my K10U crossgrade arrives. :-)

Make sure you check out the Boscomac ensembles too, some of the best Reaktor instruments and effects out there! All donationware.

Mozart did this some while ago.  He created a book which you could use in conjunction with dice rolls to build randomised waltzes.  Apparently, he understood a thing or two about music.  Very much in the same way that I do not.
 
Somebody's created a web page based on this: http://sunsite.univie.ac.at/Mozart/dice/#options
 
This can, apparently, create "11¹⁶ = 45,949,729,863,572,161 different yet similar waltzes"
 
It is unknown whether Mozart tested each combination ;-)

Reaktor 5 has a number of sound generators that are pretty good, some have interesting UIs as well.