This page contained a comprehensive list of all extensions that were known to work around 2018. The list has been archived on Inkscape's Nextcloud instance here. To search for extensions, use the Inkscape website's Extensions gallery or the new Extension Manager available in Inkscape 1.2 and later by going to
Manage Extensions (internally it uses the gallery to search for extensions). The extensions' documentation itself has been moved to the documentation of the extensions repository.