GTFS data for Greece, a best-effort project with many hurdles.
Only two Greek transit agencies have provided public GTFS data so far (as of 2018-01-25), the Athens metropolitan transit agency OASA and the Greek railways (Trainose). The data is very outdated (OASA) and of questionable quality (Trainose).
There are dozens of other public transport providers in Greece, who cover big parts of the country and provide important services, but do not provide any open GTFS data or any data at all. The purpose of this project is to collect, standardise, publish and refine the data, with or without their cooperation.
The original OASA data are licensed under the CC BY-NC 4.0. The original Trainose data are subject to their own license, which has not been published. The intention of Trainose appears to be to place the data in the public domain, but that's only an assumption. You use that data at your own peril.
All patches and new additions of data are own work of their respective contributors and are published under the Open Data Commons Open Database License (ODbL). Most - if not all - geographic data in the patches and new additions are derived from OpenStreetMap.