I was looking for Cucumber projects as well. And actually there is wiki page on Cucumber's repository with a list of such projects (not all of them are still using Cucumber though):
Projects using Cucumber:
- Gemcutter
- Clearance
/generators/clearance_features/templates/features/
- WebJam
/features/
- Redcar
/plugins/*/features
- jeweler
/features
- jekyll
/features
- CarrierWave
/features/
- RadiantCMS
- OERPScenario (linked to OpenERP)
- WontoMedia
/features/
- Rails directory
- Broth
- Heroku Suspenders
- TimeFliesBy
- Diaspora
- Chef
Source: https://github.com/cucumber/cucumber/wiki/Projects-Using-Cucumber
