Affirmative

Affirmative is a fast SFV file verifier for Mac OS. It calculates the CRC32 checksum of files listed in an SFV file and compares the result with what’s stored in the SFV file.

When downloading stuff from the Internet, the archives will frequently contain a .sfv file. Just run this file through Affirmative and it will alert you if any of the files are corrupt or missing.