I'm looking around for a text that covers vector calculus and multivariable calculus, and that is also "free as in speech," not just "free as in beer." In other words, I'm looking for texts that are not just available for downloading free of charge but that are also under a license such as GFDL or Wikipedia's CC-BY-SA, so that their contents can be reused, modified, remixed, etc., even for commercial purposes. Does anyone know of any good books that fit these criteria? The only one I know of is Hoffman, Contemporary Calculus, which covers two years of calculus.
I believe Community Calculus is exactly what you're looking for. It is under a CC BY-NC-SA 3.0 license.
OpenStax textbooks are freely available under a Creative Commons license. They have a series of three calculus books, including multivariable calculus. I haven't used that book, but I have taught using their Calculus 2 book, which I found to be reasonably good in most respects (and without any really critical flaws, though there are some aspects that could use improvement).