All three are the puppet bridges from here: https://github.com/matrix-hacks. The Hangouts and Slack bridges run on the odroid, same as synapse, and iMessage runs on an old mac mini I bought off of ebay.

The docs could be better, but I didn't find them too terribly hard to set up. If you decide to try it out and need any help feel free to ask around in #matrix-puppet-bridge:matrix.org