Pimsleur is a series that produces audio-only language learning courses. Originally created by Paul Pimsleur it is now produced by Simon & Schuster. Typically there are three levels with 30 units each. Some have a plus level with 10 further lessons Others are yet to be released. The programs are built so that the recordings prompt you to recall a fact just before you forget it, thus strengthening your memory of that language fact (vocab or grammar construction.)
Pimsleur courses teach their material very well. That is, at the end of the course, the student will generally have very good pronunciation and ability to use the material to produce new sentences. However, the actual amount of program content is very small -- generally only about 500 words. When compared with the total program 45-hour runtime for a 3-part course (3 levels of 30 half-hour lessons), it is obvious that Pimsleur is not as dense as Assimil or FSI Courses. Somebody spending 45 hours with another course would probably get further in their language studies. That said, the course does succeed in getting students to respond instinctively to the small-talk situational drills.