Worth saying that Discourse is not a “paid CMS”.
Discourse is a free and open source forum software. You can download the software for free and run it from your house, and we even have written guides for it Discourse on a Raspberry Pi | Blog. The same way you can run it internally at your school or company, and it’s all free.
We do offer paid hosting, as there are many people who need a forum and need high availability or other requirements where it makes sense to outsource it to a professional service.