Hashtag Harvest finds related hashtags on Mastodon.

Are you looking for your Mastodon fam? Enter a hashtag (no # please). Hashtag Harvest will search for that hashtag across four large instances and return a list of related hashtags, as well as information about accounts with more than three mentions across the aggregated search results.

Please note: I have some rate-limiting built into this to comply with Mastodon's API, so the results will take a couple seconds to load.