nsrewrite came from Arsdigita and is in the OpenACS-customized tarball of AOLserver 3.3. A version with some new documentation is in the AOLserver CVS repository on SourceForge, but hasn't been made available through the SF file downloads yet.
A current list of AOLserver modules is available here: http://empoweringminds.mle.ie/openacs/aolserver_modules
You might also be interested in what's new in AOLserver 4: http://empoweringminds.mle.ie/openacs/aolserver4_changes.txt
OpenACS is indeed complex, but the powerful request processor is just one of its features - even if you don't use any of the drop-in applications like the blog, forums, or photo album, you might like its user management, database procs, enhanced templating, schema and API browser, testing and debugging tools, ...
Please let us know how you fare with whatever you decide!
