Some early planning notes for the pipeline, datamodels and WCS:

https://aeon.stsci.edu/ssb/trac/jwst/wiki/PipelineStepRequirementsAndDesign

The subpackage jwst.stpipe early on was forked as owl_pipe. Here's an old snapshot:

https://github.com/fpierfed/owl_pipe

The commit history of the jwst repo before being moved to Github

https://aeon.stsci.edu/ssb/trac/jwst/browser/trunk (internal STScI only)