@brad_frost Threads uses federation through activity pub (If the user on threads turns it on on their end) and while Bluesky does not, there are Bridges like @bsky.brid.gy that allow you to follow bluesky users from the fediverse and vice versa. That is how I follow bluesky and threads users from this account.

Alternately, there are apps that allow you to do something similar to @pidgin where you have accounts on the different services and can post to them from the same app.