MountainsMap is described as 'Surface imaging, analysis and metrology software' and is an app. There are three alternatives to MountainsMap for Windows, Linux and Mac. The best alternative is ImageJ, which is both free and Open Source. Other great apps like MountainsMap are OLYMPUS Stream and SPIP™.
ImageJ is a public domain, Java-based image processing program developed at the National Institutes of Health. ImageJ was designed with an open architecture that provides extensibility via Java plugins and recordable macros.