A haxie is a "hack" or system modification designed to customise Mac OS X. The term was first devised by Unsanity, the most popular being ShapeShifter. Haxies are generally unstable and prone to cause application crashes and even kernel panics. To some extent, it resembles a combination of both a system extension and a control panel (in Classic Mac OS speak). Haxies are often customised by means of System Preferences panels.