Extensive customization opportunities are provided through the use of ReaScript (edit, run and debug scripts within REAPER) and user-created themes and functionality extensions. ReaScript can be used to create anything from advanced macros to full-featured REAPER extensions. ReaScripts can be written in EEL2 (JSFX script), Lua and Python. SWS / S&M is a popular, open-source extension to REAPER, providing workflow enhancements and advanced tempo/groove manipulation functionality. ReaClassical provides a full open source environment for doing classical music editing, including source-destination editing, multitrack track-group editing and a two-lane crossfade editor. REAPER's interface can be customized with user-built themes. Each previous version's default theme is included with REAPER and theming allows for complete overhauls of the GUI. REAPER has been translated into multiple languages and downloadable language packs are available. Users as well as developers can create language packs for REAPER.