Did you fork the Nagios Plugins?

Short answer: No. They forked us.

Long answer:

Initially, there was a Nagios Plugins project. Today, there is both a Nagios Plugins project and a Monitoring Plugins project. The answer to the question of who forked whom probably isn't immediately obvious, especially for those who weren't involved in the mess. It'll depend on how exactly you define a "fork", and it may not be all that important anyway.

However, because you asked, here's our view on the happenings.

Originally, there was a Nagios Plugins project that was maintained by us; i.e., a team of volunteers not affiliated with Nagios Enterprises.
In 2011, we transferred the nagios-plugins.org domain to Nagios Enterprises on their request. This transfer was coupled with an agreement that we would continue to run the project independently.
Early in 2014, Nagios Enterprises copied most of our web site and changed the DNS records to point to their web space instead, which then served a slightly modified¹ version of our site, including the tarballs we created. This was done without prior notice. Presumably, their reasoning for this move was that we mentioned Icinga and Shinken on our home page.

So today, there are two projects:

One driven by the company that controls the domain.
The other one driven by the team that lost its domain, but that did the actual maintenance work in the past, and that continues to maintain the same project with the same infrastructure (e.g., the GitHub repositories and trackers, the mailing lists, and the automated test builds) under the new name.

Thus, in our view, they clearly forked us, not vice versa. We just see two differences to most other forks, which make this case less obvious:

The project that has been forked didn't own its domain name.
The project that performed the fork did so without showing any previous development activities.

In the meantime, they changed the contents and design of parts of their web site. ↩