Openness and decentralization are qualities of scientific culture and methodology that have stood the test of time. For science to continue to thrive, the science gateways scientists use to do their research together should be open and decentralized too. At NCSA we have developed a full-stack cyberinfrastructure called DecentCI for research collaborations based on OpenStack and Kubernetes that makes it easy to deploy a curated set of collaborative tools and services from the open source ecosystem in addition to our own custom applications and integrations. The design is driven by a desire to prioritize data ownership, giving researchers as much control as possible over their data, communications, and access controls. We demonstrate the flexibility of our platform with examples from existing projects including Dark Energy Survey, South Pole Telescope, and MUSES that range from astronomy to nuclear physics, showcasing solutions for identity and access management, messaging, data sharing, code development, high-performance computing, community building and more.