Modo is an increasingly popular 3D modeling application, and is known to be used at Valve. It has seen widespread adoption for its extensive interface customization, modeling, sculpting, painting, rendering, and rudimentary animation toolset. It is available on Windows and Mac OS and has seen innovative development since its initial release in 2004.
Properly exporting models requires you to set the unit system to Game Units for the model to scale properly. Meters per Game Unit should be set to 1.0 to avoid additional conflicts. 1 Game Unit in Modo is equivalent to 1 Game Unit in Hammer.
Models built with Metric or English units will appear 1/1000 their actual size in-game. If you have already built your model and need to convert it to Game Units, the easiest method is using the Absolute Scale tool to automatically reset the scale of the model.
Static models can be exported to OBJ file format and compiled directly with Studiomdl, without the need for exporting to SMD file format. This currently works with static props and was introduced with the Orange Box tools.
Models will otherwise need to be exported to OBJ and imported into an application that supports SMD file format.