How is the reference implementation licensed? Can I use it in proprietary applications?
The short answer is yes, you can use it in proprietary applications. You should read the COPYING file, which offers you the choice of two licenses. These are the GPL and the AFL. The GPL requires that your application be licensed under the GPL as well. The AFL is an “X-style” or “BSD-style” license compatible with proprietary licensing, but it does have some requirements; in particular it prohibits you from filing a lawsuit alleging that the D-Bus software infringes your patents while you continue to use D-Bus. If you’re going to sue, you have to stop using the software. Read the licenses to determine their meaning, this FAQ entry is not intended to change the meaning or terms of the licenses.