It is often helpful to be able to obtain a good cryptographic checksum of a file, e.g. the SHA-256 hash. This can be used to verify file integrity, so long as you have a reliable source for the hash.
Support for both SHA-256 and MD5 from the command line are provided by default in Ubuntu and probably other flavors of Linux and BSD via the sha256sum and md5sum programs.
On a Mac (10.5) I see the "md5" command-line program, but nothing for SHA-256. Given the hash collision problems with MD5, it is a less-than-ideal choice.
And I can't find any software installed by default on Windows to compute any crypto hashes. The closest to "standard" I've seen was a Microsoft reference to how to download an optional command line program, File Checksum Integrity Verifier utility which can do SHA-1 (which is still relatively safe), but not SHA-256.
One download that I've run across for SHA-256 is hashcalc for cross-platform GUI support, but I haven't vetted it or tried it.
Am I missing any default secure hash software (better than MD5) for Windows or Mac?
Is there a page somewhere that gives good hashing tool advice for a variety of operating systems? Ideally it would lead to safe, convenient GUI solutions.
Clarification: I'm looking for advice I can share with others, which will help them safely work with hashes. By "safe" I mean something which, for example, a government employee could relatively easily determine to not be too risky. For example, software installed by default, documented and backed by the vendor, is much less risky than installing some third-party executable off the Internet. If it has to be third-party software, then something that is vetted and recommended by experts is preferred.