 MIT-licensed software can also be re-licensed as proprietary software, which distinguishes it from copyleft software licenses., MIT was the most popular software license found in one analysis, continuing from reports in 2015 that MIT was the most popular software license on GitHub, ahead of any GPL variant and other free and open-source software (FOSS) licenses.Notable projects that use the MIT License include the X Window System, Ruby on Rails, Node.js, Lua and JQuery.