Comparison of free geophysics software

This is a list of free and open-source software for geophysical data processing and interpretation. The list is split into broad categories, depending on the intended use of the software and its scope of functions.
Notice that 'free and open-source' requires that the source code is available. Simple being 'free of charge' is not sufficient—see gratis versus libre. The reader interested in freeware (just free of charge) software is referred to the list of freeware geophysics software.
Reflection seismic processing packages.
These are full-featured reflection seismology processing packages, with support for modeling, imaging, and inversion. They are relatively low-level and in some cases have their own data formats and involve learning an extensive syntax or meta-language.
Reflection seismic processing utilities.
These packages offer some subset of functionality of the full processing packages in the previous section.
Not true free and open-source projects.
The following projects are not free and open-source. They have unknown licensing, licenses which place some restriction on use or redistribution, or depend on non-open-source software like MATLAB, and thus do not meet the Open Source Definition from the Open Source Initiative. (For example, the license may rule out use by certain people or for certain purposes, e.g., in a commercial context.) They are included here because they may be of interest for those in an academic environment or access to tools like MATLAB.
Probably defunct projects.
The following projects have seen very little activity for more than a year.