RainbowCrack is a general propose implementation of Philippe Oechslin's faster time-memory trade-off technique.
In short, the RainbowCrack tool is a hash cracker. A traditional brute force cracker try all possible plaintexts one by one in cracking time. It is time consuming to break complex password in this way. The idea of time-memory trade-off is to do all cracking time computation in advance and store the result in files so called "rainbow table". It does take a long time to precompute the tables. But once the one time precomputation is finished, a time-memory trade-off cracker can be hundreds of times faster than a brute force cracker, with the help of precomputed tables.
Some ready to work lanmanager and md5 tables are demonstrated in Rainbow Table section. One interesting table set is the lm configuration #6 tables, with which we can break any windows password up to 14 characters in a few minutes.
My Rating on this: 4/5 (Quite Limited on the MD5 table compared to what you can do with LM and SHA allover power little app)