It's been 5 years. Time for another update.
MapForge has grown a lot in that time. Hexgrids are supported in both orientations, and the app can now make isometric maps, too, and edit Donjon-generated maps. There are also drawing tools, which work with either flat colors or textures.
There are now 52 free content Add-Ons to get new users started with a hefty asset library covering all the major game genres (Fantasy, Sci-Fi, Modern Day, and Post-Apocalypse). An additional 160 Add-Ons are available for purchase, also covering all the major genres.
59 content Add-Ons can be used commercially/published, the rest are for Personal Use Only. 13 Add-Ons support the Day/Night feature.
I'm currently trying to further improve support for the Modern Day genre, if anyone's interested in that. More details on the MapForge website.