What is a "sounds like" thesaurus called?
Solution 1:
Like Mitch says, you're probably looking for a Rhyming Dictionary.
You can find many Rhyming Dictionaries over the internet. Rhyme Zone 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.
Solution 2:
I will offer a slightly more Information Technology-based answer.
SOUNDEX:Soundex is a phonetic algorithm for indexing names by sound, as pronounced in English. The goal is for homophones to be encoded to the same representation so that they can be matched despite minor differences in spelling.
http://en.wikipedia.org/wiki/Soundex
dictionary here:
http://www.litscape.com/word_tools/soundex_match.php