This used to be "Anagrams" but when Apple dropped Rosetta with OS X Lion it was no longer accessible on Intel Macs. I had been a long-time user and searched far and wide for a suitable alternative: no luck. Now I'm delighted to find that it has been re-incarnated by its developer, Andrew Trevorrow, through SourceForge.
Ag is very easy to use, versatile, and fast. It will first search for all words of whatever length you choose that can be created from the letters of your input text. Then with one click it will find anagrams that use all the input letters, giving you the choice of how many words they can contain. It comes with a variety of "lexicons" - word lists - in several languages. The English lexicon has over 170,000 words but if you want more you can easily add them!
Thank you Andrew.