This free software is a Windows command-line version of UnRAR, created by RARlab, the same company that created the commerical WinRAR software. This software can extract newer RAR v5.0 file archives that aren't supported by competitors.
This free software is a Linux version of UnRAR that is based on an old version of RARLAB's UnRAR with permission from author Eugene Roshal. It is licensed under the GPL. It does not support the RAR3 format.