NZB Completion Checker lets you check if a file is completely available on a usenet/newsgroup server. The check is multi threaded for speed. When the check has completed, you will be presented with some stats, that helps you to decide, if the NZB file is complete enough for you to download. For people who pay for each downloaded GB, this could save them some GB = $$$.
The lastest edition support splitting the NZB file into two files. One with all the regular files, and another with the PAR2 files. This way you only have to download what you need. If the NZB is complete, then why waste bytes downloading the PAR2 files?