You can download the latest versions of MistServer open source here. For MistServer Pro downloads please go to My downloads after logging in. The Raspberry Pi images are an image of arch linux and work on both Raspberry Pi 2 and 3. The standard login is alarm/alarm and root/root. We recommend changing these to your own preference on your first boot. You can immidiately start using MistServer by connecting to the MistServer interface.
If you'd like to compile MistServer open source for yourself you're welcome to do so. You can find the source on our Github page.