Oh nice. I just looked at the main site and the pricing page. No mention of open source anywhere there. The pricing page mentions a "free version" but also ask me to enter my email to find out more.
The license is GPL3. But they don't seem to want people to know that...
So I'm not really sure what the deal with the paid plans is. Are you just paying for them to handle hosting? Or are some features restricted unless you pay (the software is not fully open source)?