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Mercurygram | Telegram FOSS with UnifiedPush support.
(f-droid.org)
F-Droid is an installable catalogue of FOSS (Free and Open Source Software) applications for the Android platform. The client makes it easy to browse, install, and keep track of updates on your device.
Matrix space | forum | IRC
Never heard of unifiedPush, but looks great. Is it becoming standard for self hosted push notifications? I need to take control of my own notifications...
Ntfy is pretty standard, so... Yes. It's an implementation of this specification.
Ntfy is pretty common