Login with another XenForo installation's account.
2. Basic data sync at registration
3. Support login with more than one other XenForo installations
4. Open source: https://github.com/xfrocks/bdApi
bdApi - [bd] Api add-on for XenForo
0. The other XenForo installation must install [bd] API (http://xenforo.com/community/resources/1732/)
Power up your XenForo installation.
1. Upload files and directories inside `upload` to XenForo's root directory. Select "Merge" for everything if you are asked
2. Import the .xml file using XenForo add-on importer
3. Configure options in AdminCP > Home > Options > [bd] API Consumer. You will need a client ID and Secret created from the other XenForo installation.