Evertune

[3] In the late 1980s,[citation needed] Gibson developed a system called the Gibson Robot Guitar which used an onboard computer, motors, and a battery to keep the instrument in tune,[4] but the system was complex and did not gain much marketplace acceptance, according to one report.

[1][3] The mechanical device maintains a constant state of tension despite changes in temperature or humidity or the exertion of pressure on the string.

[2] The chief executive officer is Mark Chayet who had previously founded a manufacturing firm named Evermark which made CDs and DVDs.

[1] Chayet provided some of the initial financing for the firm, and other executives and entrepreneurs include David Weiderman, William Quigley, and Brock Pierce.

[6] One report suggested that EverTune will be available on a "wide range of electric guitars" in the near future and will be available as an installation kit.

Bending strings during an electric guitar solo can change a string's tension, causing it to go out of tune.
The EverTune mechanism keeps a string's tension constant by using a spring and lever system.