As the name suggests, the Audiobook Builder app allows you to combine audio file, create chapter stops, and then end up with a .m4b audiobook file. With an easy drag and drop interface, you can take dozens of audio files and send them to iTunes as a single file. Since it uses the .m4b extension, your iPhone will recognize it as an audiobook and remember playback position. You can also use variable playback speed as well. Not something you will use everyday, but it’s a godsend when you need it!