The game is written in the Python programming language, and is licensed under the GNU General Public License, although the game incorporates other free and open-source code under other licenses. The game's included song files and some internal fonts are proprietary, and their redistribution is not permitted outside of the Frets On Fire executable.
Frets on Fire is a video game that imitates the commercial game Guitar Hero. It is playable on Windows, Linux and Mac OS X. The player presses buttons in time to coloured markers, which appear on-screen, the markers are matched with the rhythm of the music. Frets on Fire can be played by using a keyboard by pressing the fret buttons and pick buttons, although there is support for joysticks, meaning that with the appropriate adapter and/or software, various guitar-type controllers can be used as well.
Coloured square-shaped markers appear on the player's screen, synchronized with the song and are played by holding the fret buttons that correspond with the correct colour and pressing one of the pick button at the correct moment. Every ten correct hits increase the score multiplier, which multiplies the points for every hit by up to four times. The multiplier is reset when the player misses a note or strums at the wrong time.
One popular version of the game is Frets on Fire X (commonly abbreviated FoFiX), a fork developed from a series of mods of version 1.2.451 of Frets on Fire. As well as having support for 4 players, this fork supports custom graphical themes (which enables users to create a Guitar Hero or Rock Band look-alike), bass and drum tracks and preliminary support for lyrics. The latest stable version of FoFiX is 3.121 released on December 7, 2009. Currently in development for version 4.000 is the inclusion of Online-Multiplayer, Video Background Support, and support for both Guitar Hero and Rock Band styles of play among many others.
The University of Nevada developed a modified version of Frets on Fire called Blind Hero which uses a haptic glove to make this game accessible to players who are visually impaired.
A similar game has been developed as homebrew for the Nintendo Wii named Guitars On Fire, which uses Frets of Fire songs, and incorporates the use of the guitar controller.
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