I created a Prolog Editor for NetBeans IDE 7.0, which meant no more than updating the GeeWhiz Prolog Editor. It provides a few cool features, as can be seen below:
I have also installed the Prolog Editor into other applications on the NetBeans Platform, where it works fine, too. In a NetBeans Platform application, you can also take a JEditorPane and bind it to the "text/x-prolog" MIME type provided by the Prolog Editor, which will enable the syntax coloring to be applied to your JEditorPane.
Get it here. Feedback welcome.