Insert GUID service uses the Mac's shell program "uuidgen" to generate a GUID/UUID and inserts it at the cursor. Using this service saves you from having to run terminal, execute uuidgen and then copy the output. A GUID or UUID (Globally Unique Identifier/Universally Unique Identifier) is a special identifier often used in software development to identify something by a number that should be unique in most any context. GUID is Microsoft's implementation of UUID but they are essentially the same thing.
Version 1.1: Added icon to service