Where did Yoko come from?

The original source code of Yoko was contributed by IONA, it is based on IONA's Orbacus product.

I currently use OpenORB, but development there has stalled. Should I switch to Yoko?

The only remaining developer of OpenORB is on the Yoko team, and no major development effort will be directed at OpenORB.

Yoko does not currently implement all the features that OpenORB has. Most notably, many of the services that OpenORB implements (Notification, Trading, etc.) are currently not available in Yoko. If any missing feature prevents you from migrating, please file a feature request in Yoko's issue tracker.