Does anyone have a solution for creating user entered #tags that store into a bucket and can be used by other users later?

The idea is akin to CMS tagging functions, with a typeahead field. I see that typeaheads are not a selectable field in forms, except for existing buckets like Portfolios or Programs.

I would like users to be able to select multiple tags, or create their own, rather than limiting it with a pulldown, a checkbox, or radio buttons.