Old ExtJS documentation, hosted here for convenience because Sencha doesn't host them anymore.
http://chris-martin.github.io/extjs-docs/
Pull the gh-pages branch:
git clone https://github.com/chris-martin/extjs-docs.git
git checkout gh-pages
Since the Ext docs webapp uses ajax, you also need to run a simple web server to use it. For example,
python -m SimpleHTTPServer 3000
Then you should be able to go to http://localhost:3000 and view it.