Is it possible to allow a user choose tags in admin panel using checkboxes? The system I'm building requires a flexible taxonomy, where users should be able to add new taxonomy stuff to entries really easy and freely as soon as the need arises. So tags seem to work best for this situation.

However, there's a usability issue I'm concerned about. And that's a lot of typing, potential typos, and general "closeness" of what's already available to users (existing tags already added by users)

What I would ideally like is a tag field, which would still allow standard entry, but which also has a checkbox list of all existing tags as well - so users could just quick check tags they want to add to an entry - without typing anything - and add any extra tags manually only when these are needed.

Would something like that be possible to implement in Craft?

(The system will be an internal one, so there's no worry about too many users adding too many tags. Eventually, every single required tag will be created at some point, and users will be able to just choose from checkboxes - that's the ideal vision of how things would work on the data entry side)

thanks!
Any reason why you'd choose tags over categories? 

Categories seem to be more of what you're describing:


  Eventually, every single required tag will be created at some point.


And since Craft 2.5, authors can easily create categories right in the Entry screen as well as pick the category they want if it's already created. No manual typing required if it already exists.

Tags are usually looser approximations of the content and are considered by content strategists to be more of a "folksonomy". 

If you wanted to push forward with checkboxes as tags, you could probably create a custom field that spits out all the tags as checkboxes, along with a way to add new ones.