Development of the core code had slowed since 2011. By 2013, most of the core developers were no longer contributing, usually due to busyness with work or their families.  In 2014, a user took it upon himself to update the core code to make it compatible with PHP 5.4+. He released LMNucleus, a backwards-compatible fork of Nucleus. 
gRegor Morrill took the initiative to contact the core developers of Nucleus to see if the project should be sunset and people directed to use the LMNucleus fork instead.  After confirming there were no objections, and realizing no other core developers were active, it was decided to sunset the project. The nucleuscms.org website would remain online and direct people to related projects, such as LMNucleus. The sunset announcement was posted on June 14, 2014. 
In July 2014, the Japanese Nucleus community expressed interest in continuing development of the core Nucleus code . In response, the developer of LMNucleus announced his development was put on hold because he did not want to compete with a continuation of the core code.
In January 2016, the Japanese Nucleus community took down the sunset message on nucleuscms.org, posted an updated version of Nucleus CMS along with plans for the next release, and re-opened the forums. 
- Webmention plugin developed by gRegor Morrill
- As of 2015-07-12 I am no longer using Nucleus CMS on my site or maintaining this plugin. If you would like to continue maintaining this plugin's code, I'm willing to transfer ownership of the repository. Pull requests and forks are also welcome.
- gRegor Morrill used it on gregorlove.com from 2002 to 2015, then migrated to ProcessWire
- Contributed several plugins and core developments.