Q, to me, looks like a fully refundable, fully changeable coach fare. I have been booking these often in the past 2 months because I really do change flights a lot (especially last-minute!) and I'm finding that they are my best overall value for my business travel.

I see it listed as "moderate restrictions", but I'm not sure what the restrictions are. The full fare code for my flights when I book at United.com is always "QRA". I wonder what the RA means...

The QRA fare is identical to the max Southwest fare on a given route, in my experience. Perhaps that's its purpose.