Download Links for Version 1.0.8
Download the Alchitry drivers here.
The Mojo drivers can be installed by running the file named dpinst-amd64.exe which can be found where you installed Alchitry Labs or in the Windows files (not the installer).
Move the 99-alchitry.rules file from the driver folder into /etc/udev/rules.d/. This will prevent the board from showing up as "unknown" when listing them off.
To build projects for the Au you need to install Vivado (WebPACK, aka free).
To build projects for the Cu you need to install iCEcube2 (bottom of the page).
If you are building with iCEcube2 for the Cu, you will need to point the IDE to your license file for iCEcube2. You can get a license here.
You can also use the open source project IceStorm to build for the Cu.
To build for the Mojo you need to install ISE.