Other extensions

PageLock
Page locking extension which can be used by other components to prevent concurrent changes.
Included in Core distribution.
Profile
User profile extension and avatar management.
Included in Core distribution.
See User profiles for further details.
OAuth
OAuth authentication provider.
Included in Core distribution.
See Authentication / OAuth for further details.
Formicula
Contact form generator

Legacy Modules not yet converted to Zikula 3.x

Several others… see zikula-modules for example