Multiple projects on board
When you have many small projects or for example many repositories composing single project sometimes it is useful to see all of them on a single board to get the whole picture of what's going on in project.
Also we should take into account multiple points of view - e.g. the same kanban board is used by managers, developers and executives, they all need abstraction level, e.g. for me as a developer I should be able to see the whole picture but should be able to see individual tasks as I am working on tasks, chief executive should be able to see the whole picture, but could not care of individual tasks, etc.
There are multiple possible solutions - simply allow to create multiproject boards, or there is approach called "portfolio kanban" which is designed specifically for such a cases. Also there is technique of linking projects, but this becomes really messy in case of many project.
For now, we are evaluating portfolio kanban to be implemented.