The Mods feature was introduced in Tiki 1.9 as a tool to distribute, install, upgrade and remove Tiki components with LGPL incompatible licenses which didn't allow them to be included as part of the Tiki release package. A Mod can be a feature, plugin, module, theme, language file, replacement for an existing feature, or a combination of these. However, this feature is now deprecated in favor of Packages and, as of Tiki 19, it is completely obsolete, as all mods-related code has been removed in this version. Towards the end of life of the Mods feature, it has been used only for aftermarket visual themes and PluginR.
Basic principle
The Tiki Mods behaves like many package management software that is known in the unix world, and could be compared to the debian apt, the redhat yum; mandrake urpmi; or gentoo emerge, but adapted to the tikiwiki environment. It's a web-based tool for update operations on some tikiwiki extensions. It fulfills the following functions:
maintenance of locally stored mods : comparison with remote, downloading of new versions
installation of local mods, upgrade and removal
The admin mods interface can be found in tiki-mods.php, provided that you log in as admin.
More information
See Mods User for more information on how to install mods easily through the tiki-mods.php admin interface, and Mods Admin if you need manual install of mods, and further customizations.