7-Zip is a free and open-source file archiver, a special software used to put files in shrunken-down containers called "archives". It is developed by Igor Pavlov and was first released in 1999. 7-Zip uses its own 7z format, but can read and write several other archive formats. The program can be used from a command-line interface as the command p7zip, or through a graphical user interface that also works with the shell. Most of the 7-Zip source code is under the GNU LGPL license; the unRAR code, however, is under the GNU LGPL with an "unRAR restriction", which states that developers are not allowed to use the code to reverse-engineer the RAR compression format.