Nucleus CMS is an open-source blog management software package written in PHP, with a MySQL backend, primarily written and maintained by Wouter Demuynck. It is used to manage frequently-updated Web content. With a little tweaking (mainly to skins), it might be considered a lightweight content management system.
Nucleus makes use of a callback function which has led to a plugin system that has inspired somewhere in the order of 50 to 100 distinct plugins. The general drive within the development community is that functionality should exist as plugins as totally as possible. This philosophy has led to a relatively light and uncluttered base install.
Nucleus is included in Fantastico, available via many domains' cPanel as well as via a number of "easy install" services such as Simple Scripts.
Nucleus is developed and supported actively across five languages (English, German, Polish, Czech, Japanese) as well as having more than fifty user contributed translations available.
Demonstration installations of Nucleus CMS are hosted both by The Nucleus Group  and by Open Source CMS.
The English language forum has over five thousand registered users.
NucleusCMS uses a database to store content which is manipulated by a number of classes. These classes fall into two groups, core and plugin. The core contains the basic functionality including a callback system which is used to trigger plugins. By default, NucleusCMS comes with just one plugin as standard (two from version 3.3).
The output is rendered using a custom two layer substitution based template and skin system. Templates generally provide the form for iterated content (such as listings) whereas the structure is provided by what are called skins. Skins are divided up by type (index, item, archive, archives, user, error, search (and custom with 3.3)) and are specified separately to each other. Include files can be used to reduce repetition of common elements.
Nucleus CMS supports a number of common blog oriented API through the use of an XML-RPC library.
Very little of Nucleus CMS is sourced from additional parties. There are a few documented exceptions, however.
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