Is there only one program for hosting a Diaspora pod, or are there several implementations?
Diaspora is the name of one Ruby implementation for a decentralized social networking tool, just like Firefox is the name of one implementation for a web browser.
If you want one written in another language, it won't be Diaspora and it won't load any Diaspora plugins (just like Chrome doesn't load Firefox plugins) but, if it speaks the same protocols, it will be able to talk to Diaspora.
These platforms can also talk Diaspora protocol and connect to Diaspora pods:
- Hubzilla (formerly Red Matrix) (PHP)
- Friendica (formerly Friendika, formerly Mistpark) (PHP)
- Socialhome (Python)
- Pyaspora (Python)
Regarding OStatus: The answer above is not entirely correct.
Yes, there is a lot in common with OStatus (WebFinger, XRD, hCard, Atom, ActivityStreams) but the way posts are sent between Diaspora pods is somewhat different than the way OStatus platforms such as GNU Social, Pleroma or Mastodon do it.
Sharing of posts in Diaspora is not the same as "following" a feed on an OStatus platform and pods send each other Salmon slaps directly rather than via PubSubHubbub.
This document contains technical information for installing the necessary software to run a pod yourself, either for development, or as a new pod on the Diaspora network.
Hope this helps.