Tiki is the Free/Libre/Open Source Software Web Application with the longest support period

• FLOSS -> http://en.wikipedia.org/wiki/Free_and_open_source_software
• Web Application -> http://en.wikipedia.org/wiki/Web_application (This includes Wiki, CMS, Groupwares or any application comparable to Tiki)
• longest predictable support period: Tiki offers a choice of rapid release or Long Term Support (LTS). Tiki 12 LTS will be supported for 5 years. See: Version Lifecycle

• Typo3 3 years
• MediaWiki 3 years
• Joomla 2 years and 3 months
• OpenERP 4.5 years
• Nuxeo 3 years
• With WordPress, you need to always stay in a rapid release cycle even when your site has all the features you need because WordPress doesn't offer an LTS verson and this is unlikely to change because the project leader is "philosophically opposed" to Long Term Support (LTS) versions.

  
  

• At any given time, there are two major release series of Drupal which are supported. There is no fixed release schedule o it's not predictable. This being said, historically, there is a release every 3 years, and it take about 18 months before extensions are ready for an average site, so you get an effective support for 4.5 years.

  
  

• Version Lifecycle
• FLOSS Web Application with the most built-in features
• FLOSS Web Application with the most contributors with direct commit access to the whole code base
• FLOSS Web Applications with the fastest release cycles

  
  

• Free and Open Source Software Web Application with the longest support period
• FOSS Web Application with the longest predictable support period
• FOSS Web Application with the longest predictable security support period