They have a Beta version for users to test out before they make them the next official release...With this Beta series they have introduced torrent downloading using limewire as well as other things...
The betas' are always an odd number ie. the 4.13 series, when it gets officially released it will probably become 4.14...
There is also a Beta testers forum where the developers frequent, that way you can report bugs and other types of problems you may be experiencing with the latest Beta...
Bugs and Beta Testing - LimeWire Forums