Debian has three sections for packages - main, contrib and non-free.
(Not to be confused with the three distributions - stable, testing and unstable. Each distribution has the above three sections.)
The package called
diaspora was in the main section in distribution testing for a few months when we were trying to integrate it into FreedomBox back in 2017. However, it was removed from testing due to issues in its dependencies.
There is a different package called
diaspora-installer which installs diaspora on a Debian system by downloading ruby packages from rubygems.org. This happens in the postinst script of this package (runs right after package installation). A package which requires either non-free Debian packages or external packages cannot be in main. Since the package is itself free but requires non-Debian packages during installation, it is classified as contrib.
You can install diaspora on your FreedomBox using
diaspora-installer but your FreedomBox will not recognize it., i.e it is as good as a manually installed package. We can only officially support it once the package
diaspora from main becomes available.
If you decide to install diaspora manually, make sure that you configure it to run on a subdomain. FreedomBox currently doesn’t support subdomains but it is on this year’s road map.
You can search for packages on https://packages.debian.org and see if they are tagged as contrib in the results. There are two search boxes on the page. Use the one near the bottom.
For example, these are the search results for package