Track Concatenator converts iTunes tracks into one, chapterized MP4 file. Allows for audiobook or music output. Requires FFMPEG/MP4v2 (can also be installed on the first run).
Joins MP4/AAC files without reencoding; joins filetypes (or combinations of filetypes) with MP4/AAC reencoding at the highest bitrate of the input file.
Watch the demo video Merging tracks in iTunes.
Version 3.2: