I would like to present Fitnesse to my colleagues, and I want to give them a successful project where Fitnesse was helpful. The project must be written in Java.
Unfortunately I do not have an open source project where FitNesse was helpful. I used it for a number of customers, but never in an open source project. Actually I tend to use FitNesse to test deployed software from the 'outside' (via a browser, SOAP or REST), so while my FitNesse code is in Java the systems I have tested with it have been in Java, .Net and AngularJS.
The most recent projects where I tested with FitNesse have been for Vodafone Thuis, their order portal is publicly accessible: http://thuisbestellen.vodafone.nl (written in C#), but then you don't see any of the FitNesse tests.
If you clone my fixture/baseline installation of FitNesse you will find some example tests using publicly accessible services/sites in the
HsacExamples suite. I believe they demonstrate some of the power of FitNesse beyond 'Hello World'.