Adj commands modify SVG.
One significant feature is "constraints".
The original purpose of the Adj framework has been to facilitate creation and long term maintenance of system diagrams. Adj has been designed specifically for diagrams of large complexity. Unrelated uses are expected.
Start by reading the User Guide at user-docs/index.html, also online here.
If you are here for the essential adj.js file, it is at user-docs/js/adj.js and online here.
If you are here for running the test suite, it is at user-docs/tests.html and online here.
There is a dedicated category in a blog.
A fledgling Wiki is online here.