RAR compression applications and libraries (including GUI based WinRAR application for Windows, console rar utility for different OSes and others) are proprietary software, to which Alexander L. Roshal,[4] the elder brother of Eugene Roshal, holds the copyright.
Version 3 of RAR is based on Lempel-Ziv (LZSS) and prediction by partial matching (PPM) compression, specifically the PPMd implementation of PPMII by Dmitry Shkarin.
[6] The RAR file format revision history: RARlab's native software is available for Microsoft Windows (named WinRAR), Linux, FreeBSD, macOS, and Android; archive extraction is supported natively in ChromeOS.
The software license agreements forbid reverse engineering.
The filename extension rar is also used by the unrelated Resource Adapter aRchive file format.