Cura is developed by Ultimaker to make 3D printing as easy and streamlined as possible. It includes everything you need to prepare a 3D file for printing and to print it. Cura is fully preconfigured to work on the Ultimaker and comes with a friendly setup program that helps you install the latest firmware as well as calibrate your printer.
Cura is Open Source Software based on CuraEngine – a powerful, fast and robust engine for processing 3D models into 3D printing instruction for Ultimaker and other GCode based 3D printers.
Sources can be found at github, where it is available for download for a range of operating systems, including Windows / MacOS X / Linux.