MODX started out as a volunteer open source project in 2004, but also became a company in 2010 after its first user conference. The service is focused mostly on attracting agencies that build websites for clients and emphasizes the ability to extensively customize the appearance and structure of a site.
Users can just sign up for an account and start building sites for their clients without ever worrying about what’s under the hood, but for those who want it, MODX is trying to add a much deeper layer of customization than I’m used to seeing from hosted web CMSes.