Until June of 2020, Montage was maintained in the Accurev institutional Configuration Management system at IPAC/Caltech. Even though there had been for several years a copy of the released version in GitHub, this made contributing difficult as there was an average of two years between major releases and the inevitable divergence of what current code base and what people could see.
Montage is now entirely maintained through git, with both the formally released version and a development branch (and occasional long-lived feature branches) available.
While we are open to merging certain bug fixes as patches to the released version, most contributions should be structured as pull requests to the "develop" branch.
We will make every effort to keep the develop branch in a state where it is safe to download and use, even operationally, but beware that it cannot be as fully tested as the formal releases. Montage is a fairly big package and can deal with very large datasets, so full regression testing can take weeks of computer time. For example, building a HiPS map at scale from 2MASS image data involves almost 2 TBytes for just the final image data and certain aspects of the processing can only be tested at scale. Moreover, it requires several CPU-months of processing which only makes sense on a dedicated cluster or cloud. Other modules can be tested more simply but even here the volume of data and processing time for any real testing goes beyond what is realistic for any simple Continuous Integration model.
With that caveat in mind we still advocate using the develop branch if you can for your applications. Just test your use of it first.
Of course, the majority of contributions are going to be things like bug fixes, support for new versions of compilers, and so on. Most of the Montage modules are structured with the main functionality in a C function with each main function wrapped with a command-line driver program. Most people use this set of programs but the functions are also combined into a shared-object library and that library wrapped as a binary Python extension. The library/programs are also cross-compiled into a set of Windows executables. Some modules have even been cross-"compiled" into asm.js Javascript that will run in browsers directly at near-native speeds (this is not part of the distribution and was done at SAO as part of the SAOImage JS9 project).
All of these areas are fair game for contributions. There is a very long list of things we hope to get time for but would be happy if someone else were interested it taking them on, from as simple as cleaning up the rest of the modules that don't have a library form to formalizing the asm.js functionality to building a version of the Python binary extension that works in Windows.
Montage has been used quite a bit by the IT community for research in developing workflow systems and we include some early work done with one of the more advanced of these: Pegasus by the Information Systems Institute at USC. But a lot more could be done with this, especially to make use of cloud computing.
And then, of course, there are completely new modules that could be added, either to do new things or in support of specific projects/instruments. We would be happy to advise or even collaborate with anyone interested in such an effort.