The best open source alternative to FeedDemon is FreshRSS. If that doesn't suit you, our users have ranked more than 100 alternatives to FeedDemon and loads of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to FeedDemon are Feeder RSS feed reader, Fluent Reader, RSS Guard and NetNewsWire.
FreshRSS is a free, self-hosted RSS aggregator. It is quite lightweight, fast (it can manage +100k articles without complaining) and powerful (e.g. shortcuts, filters, responsive design, multi-views, multi-themes, multi-users, statistics, provides a Google Reader API, etc.)
Feeder is a fully free/libre feed reader. It supports all common feed formats, including JSONFeed. It doesn't track you. It doesn't require any setup. It doesn't even need you to create an account!
It is free for Mac, Windows and Linux if you download it from GitHub, and it's paid ($2) for Android and iOS.
RSS Guard is simple, light and easy-to-use RSS/ATOM feed aggregator developed using Qt framework which supports online feed synchronization.
RSS reader shows you articles from your favorite blogs and news sites, and it keeps track of what you’ve read.
NewsBlur is a personal news reader that brings people together to talk about the world. It shows you the original site and allows you to read stories directly off the site while keeping track of what you read. It also filters and highlights stories you like and dislike.
QuiteRSS is a open-source cross-platform RSS/Atom news feeds reader written on Qt/C++
Liferea is a web feed reader/news aggregator that brings together all of the content from your favorite subscriptions into a simple interface that makes it easy to organize and browse feeds.
Just like its namesake, Capy Reader is a small RSS reader focused on approachability and simplicity.
This is a copy of Reeder, in order to give Android an RSS reader similar to Reeder, combines the interaction logic of Reeder with the design style of Material Design 3 (You).
A snappy, customizable video feed. Designed to show you exactly the content you want to see and nothing else.
Twine is a beautifully crafted RSS reader app. Access all of your favorite feeds in a single app.
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