Zulip is the best open-source Slack alternative you can get, and it can be hosted on your own server or use it with a paid plan.

If Windows is your OS of choice, consider these open-source apps. There are tons of open-source apps for just about any task. These are all free to install and use on Windows. I've been using ...

Windows comes loaded with software to meet most of your needs out of the box, but if you like free and open-source projects, or if you just want alternatives, there are plenty of great options out ...