We use discourse over at http://komodoide.com and I often find myself wanting to “assign” someone to a support thread. Right now I often reply and simply mention them, but this is not ideal.
Ideally I’d like to use the “flag” functionality to give it a custom flag that I could create myself, eg. “needs support with frontend”. I could imagine this functionality being very useful for a variety of Discourse implementations.
We always planned to allow customisation of flags, just have not gotten around to it.
Visual mocks and UI workflows will greatly help build such a feature.
I second this, I would really like to be able to flag discussions as open / close / pending. I think between the “Category” and the “Post” columns would look like the right place to put flags. Like categories themselves, I think color coded options would be ideal. Also being able to specify the sort ordering would be helpful.
Any update on this 
? Having custom flags would be great for my organization’s use case.
Yep. That would be a nice addition. A client of mine ist looking for a way to flag threads/messages with some kind of to-do flag. So the admin or another stuff member remember to look after the thread/message.
Bumping this because users of my community could use the flag system to report videos removed from Youtube etc. without having to type it themselves in the custom report field.
Use the official assignment plugin for this; no flags needed.
See also Creating Custom Flag.