SOPAC is a next-generation catalog system that takes advantage of online, web 2.0-like interaction to build a rich, engaging discovery layer.
What that means practically is that in a SOPAC you can rate, review, comment on and tag items in the online catalog. This technology (is it technology? maybe innovation is a better term? or revolution in online public catalogs?) was created by John Blyberg and first implemented at the Ann Arbor District Library.