There are many great open source, self-hosted options available for businesses and individuals! Here are some categories and examples to get you started:

General Purpose:

Web Server: Apache (https://httpd.apache.org/), Nginx (https://nginx.org/)
Operating System: Linux (various distributions like Ubuntu, Debian) (https://ubuntu.com/, https://www.debian.org/)
Virtualization Platform: Proxmox (https://www.proxmox.com/en/proxmox-ve)

Communication & Collaboration:

Email Server: Mailcow (https://docs.mailcow.email/getstarted/install/)
Project Management: OpenProject (https://www.openproject.org/download-and-installation/), Redmine (https://www.redmine.org/)
Team Chat: Mattermost (https://mattermost.com/channels/), Rocket.Chat (https://www.rocket.chat/platform/open-source)
Video Conferencing: Jitsi (https://jitsi.org/)

Content Management:

Website Creation: WordPress (https://wordpress.org/), Drupal (https://www.drupal.org/)
Wiki: MediaWiki (https://zh.wikipedia.org/wiki/mw🙂
Knowledge Base: BookStack (https://www.bookstackapp.com/)

Other Useful Tools:

Customer Relationship Management (CRM): SuiteCRM (https://suitecrm.com/)
Marketing Automation: Mautic (https://www.mautic.org/)
Password Management: Vaultwarden (https://bitwarden.com/help/install-on-premise-linux/)
Cloud Storage: Nextcloud (https://nextcloud.com/)

This is just a small sampling, there are many other options available depending on your specific needs. Here are some resources to explore further:

Awesome Self-Hosted: A curated list of awesome self-hosted software (https://github.com/awesome-selfhosted/awesome-selfhosted)
r/selfhosted subreddit: A community for discussion and help with self-hosting (https://www.reddit.com/r/selfhosted/)

Important Considerations:

Self-hosting requires some technical expertise for setup and maintenance.
Security is your responsibility, keeping software updated is crucial.
Consider the ongoing costs of hardware and potentially increased IT workload.

I hope this helps!