HD Moore has this to say when he sold Metasploit to Rapid7:
The challenge for open source is that, while it’s a fun hobby, how can we make it profitable — a real business? We can operate an open source project, but how can we make it sustainable?
Sure, open source software ought to be free because like it or not, it is either free software or permissive-licensed software. So how do people make open source sustainable? Let me count the ways:
1. Foundation – Linux Foundation, Apache Software Foundation, GNOME Foundation, etc.
2. Commercial backing – Metasploit bought by Rapid7, Canonical (Ubuntu), Red Hat (Fedora), Novell (openSUSE)
3. Donations – Linux Mint
4. Hmmm, reality is complex (really), so let’s just leave this research to OSS Watch, shall we?