Openvibe.social is an interesting (proprietary) app that combines 4 different social networks incl Nostr, Mastodon and Bluesky.

Here is a review by John Gruber ( though 6 months dated) https://daringfireball.net/2025/01/openvibe

'I really don’t see the point of mashing the tweets from two (or more!) different social networks into one unified timeline. To me it’s just confusing.'