There are a number of caveats, but bugsy is essentially correct in how to do it. It's those caveats that make life difficult.
I don't remember all of them, but you can't disclaim some things like moral rights (usually not applicable, but they relate to things like vandalism of the work & the right to attribution as the author and vary by jurisdiction), with some works like music, you can end up with the licensing organizations collecting royalties on it without your authorization, there are always trademark issues to consider, doubly so for some special trademarks like that of the Red Cross and the Olympics which are enshrined in laws that implement international treaties, and probably a host of other things, including strange things like common law copyrights (there was a case in NY about what should have been public domain music falling back under copyright a few years back).
So... yeah, you can disclaim your work into the public domain, but there are still gotchas out there and you need proper legal advice to avoid them even when you're using what should be copyright-free works, because there are all sorts of weird formalities like the requirement in the USA that copyrights can't transfer without a "written memorandum of transfer."
If you just want people to be able to use your software, I'd probably just use a BSD license instead of the public domain. It's permissive enough that it shouldn't create problems for anyone.
I don't remember all of them, but you can't disclaim some things like moral rights (usually not applicable, but they relate to things like vandalism of the work & the right to attribution as the author and vary by jurisdiction), with some works like music, you can end up with the licensing organizations collecting royalties on it without your authorization, there are always trademark issues to consider, doubly so for some special trademarks like that of the Red Cross and the Olympics which are enshrined in laws that implement international treaties, and probably a host of other things, including strange things like common law copyrights (there was a case in NY about what should have been public domain music falling back under copyright a few years back).
So... yeah, you can disclaim your work into the public domain, but there are still gotchas out there and you need proper legal advice to avoid them even when you're using what should be copyright-free works, because there are all sorts of weird formalities like the requirement in the USA that copyrights can't transfer without a "written memorandum of transfer."
If you just want people to be able to use your software, I'd probably just use a BSD license instead of the public domain. It's permissive enough that it shouldn't create problems for anyone.