NewzToolz is a free program that can decode yEnc, RAR, and PAR files. NewzToolz can also combine files. It contains an NZB downloader, and can be used to read and post to Usenet newsgroups.
On the File menu of the NewzToolz main window there is a “Compact Database” command. If the size of your NewzToolz database file becomes too large, you can use this command to try and make it smaller.