I made something for Mastodon: A gallery mini-app.
You can simply drop it in your Mastodon server's public folder, and it will show images from your server in a mosaic grid with infinite scroll. Supports some configuration as well, e.g. whether to limit it to only local images, or a specific hashtag, or which server to fetch from.
Mastodon federates using the ActivityPub protocol, as does Pleroma, Peertube, plume, and pixelfed. Anyone with the appropriate skills can build their own social network that communicates with the rest of the fediverse using ActivityPub: https://www.w3.org/TR/activitypub/
You can also contribute code to mastodon itself through github: https://github.com/tootsuite/mastodon
The Wandering Shop is a Mastodon instance initially geared for the science fiction and fantasy community but open to anyone. We want our 'local' timeline to have the feel of a coffee shop at a good convention: tables full of friendly conversation on a wide variety of topics. We welcome everyone who wants to participate, so long as you're willing to abide by our code of conduct.