MastoTrends does a search of Instances.Social for up to 50 instances with at least 5000 active users, selects ten of them at random, and fetches their trending link lists. Take a peek at what's hot around the Fedi. (It might take a moment to load if it's pulling a lot of links, but everything will load automatically.)

If you want to do more in-depth exploration of what's hot on Mastodon, try FediTrends!