FrostWire is a community project based on the source code of LimeWire, which means it is a Gnutella client with all the standard to peer 2 peer options.
At first there those not seem to be many differences between both projects, except maybe visually.
The only real difference with LimeWire is that FrostWire will always will be free, but will not offer a Pro version.
Laws concerning the use of this piece of software vary from country to country. We do not encourage or condone the use of this program if it is in violation of those laws.