Brief History

Paraphrased and extended from FireFox's .chart specifications:

In the early days of Guitar Hero, a ScoreHero user by the name of Turkeyman collaborated with several members of the ScoreHero community to reverse-engineer the original Guitar Hero 1 archive format. Soon after, a user by the name of Katamakel developed a user interface to rebuild these archives, while Turkeyman worked on an editor to modify the data contained within them. This later turned into Feedback Editor, which created the .chart format as its method of storing authored chart data.

Support for Feedback Editor dropped around the release of Guitar Hero 3 due to Turkeyman aiming to develop the program into a full game. Remnants of this can be seen with the inclusion of the Drums and Keys track in Feedback Editor, which were implemented before Guitar Hero: World Tour or Rock Band were announced. There was also a secondary version of .chart in development for this game known as .chart-v2. This format would have addressed the current limitations that came with designing the original .chart format for GH1/2, but it was never adopted by the community due to it only being available in Turkeyman’s game, which stopped development after the announcement of Guitar Hero: World Tour and Rock Band.

.chart was later used for Guitar Hero 3 customs after the release of Guitar Hero Three Control Panel (GHTCP). Among many other features, this tool allowed you to import .chart files into the game as custom songs.

Later, .chart was updated to support ExileLord's GH3 note type mods, such as tap notes and open notes. Due to Feedback’s outdated nature, these mechanics had to be implemented using workarounds that were extremely tedious and prone to errors and crashes. It was also around this time that FireFox began developing Moonscraper Chart Editor to re-support .chart and the new additions made to the format, as well as to make the charting process easier and more accessible.

Over time, people found exhaustion in the entire modding process for GH3, and soon a fan-game called Clone Hero began development by a user named srylain. This game read .chart files directly into the game without requiring conversion, which made playing custom Guitar Hero songs much more accessible and avoided any complicated game modification processes. This accessibility, combined with Moonscraper's own usage of the .chart format as its default, caused .chart to proliferate heavily within the scene.

Clone Hero would go on to implement its own mechanics into the .chart format, such as the format for lyrics by mdsitton, Guitar Hero Live track data, and additional features to bring drums into parity with the .mid format. The DJ Hero community has also made a proposal to introduce DJ Hero features into the .chart format.

Beyond this though, additions to the format have generally halted, as there isn't much else that is desired by a majority of people. There have also been a couple attempts at creating a revised format to address some issues that stem from legacy support, but none have caught on.