MarkAble is designed for podcast or audiobook listeners who own an Apple iPod, or who use iTunes to listen to such books.
Audiobook files bought from the iTunes Music Store or from Audible.com are 'bookmarking' - that is, the iPod (or iTunes) remembers the point of the book where you were up to, and resumes from there when you start listening again. This, of course, is vital.
However, there are many other sources of audiobooks. Such books may be in a variety of different formats such as MP3 files (for example, from podcasts, www.audiobooksforfree.com or www.telltaleweekly.com), or audio CDs or tapes you may have bought. MarkAble makes it easy to merge a large number of tracks or individual files into a few files which will bookmark on your iPod.
See also: iPod iTunes convert merge CD MP3 audiobook podcast bookmark