Zenodo is a repository for immutable versions of software that are provided with a persistent DOI for the purposes of citation and reproducibility.
Underworld can be cited via a zenodo DOI. There is a master DOI for all releases (10.5281/zenodo.1436039) and releases after 2.6.0 are automatically given a DOI _under the master_.
If you are using a development branch and wish to obtain a DOI for your specific version we ask that you contact us to make an interim release under the master DOI.
Underworld is listed under the AuScope community on Zenodo.