Hometown is launching with a few key differences from Mastodon.
local only posting is a per-post security option that lets you set whether that post can federate out to other servers or not.
Hometown is microblogging for writing, but its goal is to accept many content types for reading.
Reading more content types also helps make the fediverse better. ActivityPub supports all kinds of content, but most ActivityPub servers shoehorn all their content into Note because that's the type that Mastodon treats as first-class
If Hometown is going to be a universal reader, you're going to need better control over organizing your feeds than mainline Mastodon provides
Right now if you add an account to your "friends I like" list in Mastodon, posts from people on that list appear on that list. But they also appear on your home timeline, and maybe you don't want that!