Introduction and purpose of the IDE
MPIDE (Multi-Platform Integrated Development Environment) is an Arduino-like project of chipKIT™, which allows you to reprogram the board with different custom sketches. The IDE can be downloaded from the official site of chipKIT™: http://chipkit.net/started/
It is used to reflash the program memory of the microcontroller without an external programmer after the bootloader is programmed. chipKIT™ provides source code of their bootloaders on the GitHUB: https://github.com/chipKIT32/PIC32-avrdude-bootloader
As a difference of the other similar IDEs (like Arduino, Maple, Pinguino etc.) this one gives you the opportunity to work with different kind of microcontrollers. You don't have to change the IDE, in case you need to work with another family of microprocessor.