Website admin
In a small project, and most Open Source projects are small, you will end up having to maintain the website as well. I have wrestled with web server configuration files, hosting providers, HTML tags, understanding CSS classes and learned more details about HTTP security response headers than I ever wanted and of course none of that was actually related to the projects I worked in.
An Open Source project needs a dedicated website. It is not enough to exist on Gitlab, GitHub or the likes. Those are excellent source hosting and management services, but they do not replace the need for a proper website. A website that explains what the projects is, what it does, where the documentation is and how to get started using etc.
And someone needs to make sure it runs fine and that the contents can be read and understood.