Last night it seems the so called 'Nagios Plugins' project was cut off. The story started a decade ago when development of the plugins compatible with Nagios was taken over by an independent group of developers.
Some time later, the domain of the 'Nagios Plugins' project was handed over to 'Nagios Enterprises, LLC.' due trademark reasons. To get an idea about that, I suggest to read on the 'Nagios Trademark Truth' and 'Nagios Trademark Triumph Provides Promise To Open Source Developers, Shows Power of Community'. In the latter Mr. Galstad is cited with "This violation took more than four years and thousands in legal fees before it was finally resolved. My hope is that this can serve as an example to Open Source developers worldwide that they can overcome infringements and protect their brands if they are persistent and engage their respective communities.".
Yesterday in the evening the project members recognised that the DNS of nagios-plugins.org was moved to a different location. Now there seems to be a hosted (some may call that 'hijacked' or 'pirated') 'mirror' of the old site. Anyhow ... the content is already different from the original one or maybe changed even more in the future. From my point of view this can serve as an example to Open Source developers worldwide that they can be obstructed by (trademark holding) companies even if those companies profit from the work of them. So please don't use downloads from there, even the release tarballs maybe modified.
The news all about that: 'Nagios Plugins are dead, we now have Monitoring Plugins in place!"
Be sure you download your tarballs from https://www.monitoring-plugins.org/download.html and verify your checksums!