This is something that I am struggling with, I am yet to find a MongoDB GUI tool that I personally or the team I am working with are happy with. Personally I would prefer something that can be run locally (so either desktop app, or web app with integrated web server/easy setup). In regards to support for other databases, my personal view is do one thing and do it well, there is enough complexity in getting it right with MongoDB before you worry about any other databases.
This is something that I have personally been planning on building for a while, so if this were an open source project, I would be interested in contributing.
This is something that I have personally been planning on building for a while, so if this were an open source project, I would be interested in contributing.