Similar_entry is a project mainly written in Python, it's free.
Searches for semantically similar tweets.
requires: python-calais http://code.google.com/p/python-calais/ simplejson http://pypi.python.org/pypi/simplejson
Tested with python 2.6, although python-calais only supports 2.5.
Run: python run.py
Test: python test/test_all.py