At the moment there isn't a category picker available out-of-the-box in the current release of Aikau (which at the time of writing is 1.0.85) however there are a number of options available.
The first is to use one of the existing generic picker widgets, I would recommend the SimplePicker. You can configure this to publish a request for data to display as options. The ManageAspectsService provides a good example of how you can do this (the link should take you directly to the appropriate section of the source).
You can either use the CrudService or a custom service for retrieving the category options.
At some point in the future we may provide a dedicated category picker, or maybe you'd like to contribute one via pull request to the Aikau project? That way the Aikau team will need to support the widget and it will be future proof for its continued use.
Retrieving data ...