First, the two losers:
* dbus-ruby: It wraps the C bindings. It is dead (last release in January 2005).
* pr-dbus: No releases, last SVN commit in April 2007, entirely in Ruby.
Now for the contenders. Both are packaged as RPMs in the OBS YaST:Web project.
The developers know about each other but in 2007 they did not want to merge the projects. The developers are not active but patches do appear.
* ruby-dbus
- LGPL
- no test suite (but I've started one together with bug fixes: Github clone)
- can export services
- cumbersome API (explicit introspection calls needed, explicit types for variants needed, return value must be an array)
* rbus
- GPL
- test suite (RSpec, needs a patch)
- cannot export services