SAGA GIS is free software with a lot of tools. I can use a lot of data format. This is a good tool to make NMT. You can analyze areal and satellite picture.

SAGA is an open source tool, designed to load vector objects or trace points, lines, polygons and manipulate them by simple or complex analysis methods, these can be liquid flow simulations, motivated by rain, ocean currents, evaporation and others. Other models that can be cited as the simulation of particle erosion, maximum entropy, the management of photogrammetric composition of remote sensing images SAGA includes within its models, the concepts developed by Morgan, Finney, Duzant, Burrough, Hugget, among other professionals dedicated to quantitative geography. SAGA saves equipment resources focusing its effort on data processing and not on visualization with a high level of aesthetics, allows QGIS to be used as a visualizer of the results of the processes and allows the user the possibility of obtaining a product . Graphic printing of higher quality. SAGA can be compared with Esri Arc ToolBOX, since it presents the same performance with very similar results.

It's functional and useful (and open source!) GIS software. I find it intuitive and fairly well supported. I appreciate SAGA's ability to interface with other open source software including R, and it is a major part of my goal to use mostly open source software.