The simplest and easiest way to get Mu is via the official installer for Windows or Mac OSX (we no longer support 32bit Windows).
The current recommended version is Mu 1.1.0-beta-5. We advise people to update to this version via the links for each supported operating system. All previous beta versions of Mu can be downloaded from here.
On Linux, in order for Mu to work with the MicroPython based devices
you need to ensure you add yourself to the correct permissions group
uucp groups). Also make
sure that your distribution automatically mounts flash devices, or make
sure to mount them manually.