This is a launcher that mimics some parts of the Sailfish OS. It lets you get a taste of what it will be like so you can see if you would like to dive in and install the whole OS on your phone replacing Android.
The OS is only available for the nexus 4 right now but they will soon release a development kit so that it can be ported to many more Android devices. In the meantime we have the launcher. The beta for the launcher will start in august.
For more info about the launcher see
and here on xda forums about sailfish rom