Headscale is open source Tailscale.

Calcom is a flexible scheduling application whose extensive options allow it to be tailored to the user’s needs. With its ability to sync with other apps, Calcom makes scheduling efficient and ensures that appointment slots remain conflict-free.

Element is a secure and reliable real-time communication app supporting messaging, voice, and video.

Vaultwarden is a self-hosted password manager and auto-filler. In addition to being a great place to store credentials in an organized way, Vaultwarden is end-to-end encrypted and is able to sync across devices. All this in a lightweight and easy-to-run package!

Nextcloud is a collaborative office suite, file storage, and communication platform.

Jitsi is an easy to use, open-source video conferencing solution with a focus on privacy.