  This work describes the setup of an advanced technical infrastructure for
collaborative software development (CDE) in large, distributed projects based
on GitLab. We present its customization and extension, additional features and
processes like code review, continuous automated testing, DevOps practices, and
sustainable life-cycle management including long-term preservation and citable
publishing of software releases along with relevant metadata. The environment
is currently used for developing the open cardiac simulation software openCARP
and an evaluation showcases its capability and utility for collaboration and
coordination of sizeable heterogeneous teams. As such, it could be a suitable
and sustainable infrastructure solution for a wide range of research software
projects.
