• Both are full-featured free and open source web applications with which you can realize a very diverse variety of projects.
• Both are written in PHP and use a database such as MySQL
• Both can run on standard, inexpensive hosting.
• Both have large & vibrant communities
• Both use the Smarty template engine.

• Tiki is more centralized. Tiki is the all-in-one model while Xoops (like Joomla!) is the small-core-and-add-what-you-need model. Each model has its pros & cons.
• Tiki is Wiki-centric. Please see (if) Why Wiki Syntax Is Important to your project.
• Xoops 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.

Compare them at http://cmsmatrix.org

https://www.openhub.net/p/_compare?project_0=XOOPS+Dynamic+Web+CMS&project_1=Tiki+Wiki+CMS+Groupware

• How CMS architecture affects dev communities - A case study of WordPress, Drupal, Tiki Wiki and XOOPS

  
  

• Xoops
• TikiWiki vs Xoops