Similar

• Both are full-featured free and open source web applications written in PHP with which you can realize a very diverse variety of projects and use with a database such as MySQL.
• Both can run on standard, inexpensive hosting.
• Both are community-run projects

Different

• Tiki is more centralized. Tiki is the all-in-one model while Joomla! (like Drupal) is the small-core-and-add-what-you-need model. Each model has its pros & cons. Because of these design choices, Tiki has more features out-of-the-box. With Joomla, you can add tons of features via extensions.
• While Tiki is a very large and popular project (over 200 contributors to main code base and tens of thousands of installs), Joomla! is several times larger with millions of installs.
• Tiki is Wiki-centric, whilst Joomla! is more web publishing centric. Please see (if) Why Wiki Syntax Is Important to your project.
• Joomla! has extensions for features that Tiki doesn't have, ecommerce for example
• Joomla! is GPL, Tiki is LGPL. The main difference between the GPL and the LGPL is that the latter can be linked to (in the case of a library, 'used by') a non-(L)GPLed program, which may be free software or proprietary software.

CMS Match

http://www.cmsmatch.com/compare/content-management-systems/9+1073

CMS Matrix

Compare them at http://cmsmatrix.org

Ohloh

Alias

• Joomla
• Joomla!