UPDATE: I'm leaving the post here but the action described has been reversed and the project continues to live at https://github.com/charliepoole/nunit-summary
NUnit-Summary is an "extra" that I've maintained personally for some time. It uses built-in or user-supplied transforms to produce summary reports based on the results of NUnit tests.
I have contributed it to the NUnit project and we're working on updating it to recognize NUnit 3 test results. The program has never had a 1.0 release, but we expect to produce one soon.
This old post talks about the original nunit-summary program.