Portainer being an open-source software, we decided to use the GitHub platform to host our codebase as well as our issue system. No need to present GitHub nowadays, it's perfectly geared with all the tools you need to manage small to large open-source projects (albeit with the usage of integrations that are easily available via its marketplace).
In the context of the Portainer project, I'd like to highlight the tight integration of GitHub with Semaphore CI system. By leveraging this integration, we are able to automatically trigger a build of the application when a contribution is made to the project. This build is actually composed of a compilation of the program as well as the automatic creation and deployment of a Docker image directly on the DockerHub.
This allow us to easily test and validate contributions made to the project and is a must-have for any open-source project that can leverage it.