Collection of excellent open source (web) applications.
Chat / Messaging
Revolt - Find Your Community
Revolt is the chat app that’s truly built with you in mind.
Gotify · a simple server for sending and receiving messages
a simple server for sending and receiving messages

CMS
Ghost CMS
My favorite open-source CMS for content sites

Development
GitHub - TestLinkOpenSourceTRMS/testlink-code: TestLink Open Source Test & Requirement Management System
TestLink Open Source Test & Requirement Management System - TestLinkOpenSourceTRMS/testlink-code
Home
Home Assistant
Open source home automation that puts local control and privacy first. Powered by a worldwide community of tinkerers and DIY enthusiasts. Perfect to run on a Raspberry Pi or a local server.

Hosting
Dokku: Open source Heroku alternative
Dokku is a self-hosted open-source PaaS similar to Heroku.

GitHub - 9001/copyparty: Portable file server with accelerated resumable uploads, dedup, WebDAV, FTP, TFTP, zeroconf, media indexer, thumbnails++ all in one file, no deps
Portable file server with accelerated resumable uploads, dedup, WebDAV, FTP, TFTP, zeroconf, media indexer, thumbnails++ all in one file, no deps - 9001/copyparty