Chris Trottier@tokyo_0 Calckey supports comment threading. Mastodon doesn't. If you want to use comment threading with Mastodon, you have to use either an alternative web front end like @phanpy or a mobile client like @trunksapp.
As for what it does that Mastodon doesn't... a lot!
Quoted posts, groups, galleries, antennaes, clips -- those are just top of mind.
Also, Calckey has content migration. You can indeed import your Mastodon posts.
All GNU social JP content and data are available under the