Stars Without Number has a whole bunch of useful resources, especially if you're running a sandbox game. Is adventure creation tools are particularly handy, but even things as simple as its random name generators are helpful.
I've also used the collaborative system in Diaspora (a FATE game massively influenced by Traveller) to create a setting with my players which we could then play in Traveller. We used Classic, but Mongoose would work too. It's a neat way of doing things. You get a cluster of a few worlds that have pretty well-defined relationships to one another and a whole bunch of conflicts and troubles brewing.