Like Mitch says, you're probably looking for a *Rhyming Dictionary*. 

You can find many Rhyming Dictionaries over the internet. [Rhyme Zone][1] is a particularly good one, since it groups results into syllables, which can be helpful for poetry writing or any similar activity.

A google search of Rhyming Dictionary software could get you something useful, although most of the software I found cost money, so you may have a bit of trouble there.


[1]: http://www.rhymezone.com/?loc=bar