[Edit: The release version of Facebook Home can now be found in this topic.]
A pre-release version of Facebook Home has leaked ahead of the planned 12th April Play Store release date (also the release date for the HTC First 'Facebook phone').
The build itself (pulled from a pre-release HTC First ROM) seems to be rather buggy and incomplete (I can't get 'Chat Heads' working for example), but it's interesting to have a play with to see what Facebook has in store for us later this week.
In order to use the leak, you need an Android device with a maximum resolution of 1280x768 and the ability to completely uninstall your existing Facebook app. This is important, as the leaked APKs are re-signed and can't just be installed over the top of an existing installation. This will automatically exclude some devices which have Facebook installed in the base ROM. If you're on a Nexus device you're good! Even if you do have Facebook in ROM, provided you are rooted there are workarounds - i'll detail these in the comments. If you have any problems installing post below and i'll help if I can.
The leak itself is 3 APKs - the main 'katana' Facebook app: DOWNLOAD (ROMraid), the now-integrated-with-your-SMS 'orca' Messenger app: DOWNLOAD (ROMraid) (orca) and the 'home' Launcher shell app: DOWNLOAD (ROMraid). Simply install all 3 and you're set - bear in mind you do so at your own risk!
In the settings you can find some interesting options such as whether to hide the notification bar by default or not (if it is hidden, sweeping down from the top of the screen reveals it). Let us know your thoughts! :)
[Edit: It's just been pointed out to me that the original leak was signed with test keys, which could present a security risk. With that in mind i've re-signed the APKs with my own private key for peace of mind and updated the download links.]