As of 2014-01-04 the master branch will run on Mac OS X 10.11 (It will not build on 10.10. It currently builds against the 10.6 SDK, but still relies on deprecated frameworks.)
The yosemite branch builds and runs on OS X 10.11.
You can download a binary of the OPML Editor built from the master tree here: Download OPML Editor v10.1b21.