DropHash is a Mac OS X application for computing hash values for files.
At many download sites, you'll see hash values with labels like "MD5" or "SHA-1". Once you have downloaded one of these files, you can compare the hash published on the server with the hash computed from the file you downloaded. If they match, then you got the file correctly, otherwise it was damaged or has been tampered with.
DropHash is a thin GUI wrapper around OpenSSL, a free program included with Mac OS X. Many users will find this interface preferable to having to fool around with Terminal commands. DropHash is a Universal Binary and requires Mac OS X 10.4 or later.
Here's the SHA-1 hash for DropHash.zip: bdcdf7f3ed8c07c744494ff14116d5ae9bf889d4