I recently discovered an older (but still very useful) hex mapper, Hexographer. While it is capable of building simple-but-useful Subsector and Sector maps, it’s planetary maps that the Free Java-based program excels at. It is originally meant for the Fantasy Genre, but it can be re-purposed for Traveller.
The Pro version is pricey, with the price going from Free to $31.95 to get the ability to add icons, run stand-alone (instead of being tied to the Internet), add new terrain types, etc.
At the store, you can also get Cityographer (low-tech/medieval icons native: Futuristic, Modern and additional Medieval icons cost extra) and Dungeonographer (which can be used to design starships, with Futuristic Icons).
But the Real Imperial simply must get the Coat of Arms Design Studio. What’s the use of an Ancient Family Name and Vast Hereditary Lands without the right shields, symbols, flags, and associated paraphernalia?
Note that all of the above programs come in Free and Pro versions.