Open source software is about collaboration (more eyeballs checking that code!). Wikis are all about collaboration. So it'll come to no surprise that we try to leverage existing technologies and partner with others instead of reinventing the wheel.
Tiki partners with the following technologies:
Graphviz is open source graph visualization software.
Morcego is a 3D graph browser that allows users to view and navigate any graph-like structure. Examples: social networks, site maps, hierarchy or genealogy trees, etc.
PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML.
Smarty is a template engine for PHP. More specifically, it facilitates a manageable way to separate application logic and content from its presentation.
Zend FrameworkZend Framework is based on simplicity, object-oriented best practices, corporate friendly licensing, and a rigorously tested agile codebase
Please also see: http://mods.tiki.org/