Chamilo is an open source LMS with a tight-knit international community of developers, users, and HR professionals built around it.
If you’d like to go the open source route, Chamilo is one of the best-rated learning management and collaboration systems out there. Like with any open source tool, It would require you to do the installation yourself and configure your own servers, which is certainly a cost that needs contemplating. Other than that, the software is free to use and there is a very active community of users that supports the project and offers guidance in the face of any issues. As to the software itself, it’s a powerful and customizable LMS.
Completely free and for as many users as you like, you just have to consider the costs of setting up and maintenance, since it’s self-hosted.