Wallabag

Free open source alternative to Pocket and other article-saving services. There are apps for Android, iOS, Windows, Linux, Firefox, Chrome, Kindle, Kobo and others. It is also compatible with RSS readers. You can self-host your own instance for free, or use the paid-for flagship instance.

Fediverse account:
@wallabag@social.tcit.fr

AntennaPod

Free open source podcast player for Android devices. The app lets you listen to podcasts, keep track of episodes and manage your podcast subscriptions through open standards like RSS.

Fediverse account:
@AntennaPod@fosstodon.org

Gancio

A free open source collaborative online calendar. It allows local communities to share a common calendar that anyone can post events to, even people without an account. (Posts are moderated to prevent spam though.) You can also interact with Gancio through the Fediverse, and it has RSS support for people who want to follow through feed readers.

Fediverse address:
@gancio@mastodon.cisti.org