TASC Chess Tutor(tm) on the "TASC Chess CD ROM", (US$65 distributed by ICE on their products page ), is an amazing product. It's claim to be able to raise the tactical strength of the student is certainly true. It starts at the absolute most basic level (how the pieces move), up to subtleties of strategy.
Primarily the focus is tactics, although it does (in a cursory fashion) cover opening development. So most of the material is of the middle game and ending phases.
The TASC Chess Tutor consists of five steps (1-5), and each step has 10-20 lessons. Each step represents a level of tactical development. Step 1 is the easiest, and Step 5 is the hardest. The lessons start with lecture material accompanied by a board to watch move sequences. The lecture VCR-like controls make it easy to back up and go forward for repeating difficult concepts.
After the lecture material, comes the fun stuff! Each lesson in addition to the lecture has between 2-8 exercises. Some of the exercises are titled (e.g. "pin"), but most (after step 2) just say "test". Each exercise has 10 puzzles. These puzzles are conducted on the same board that the lecture is. Many of the puzzles are multi-move. So it takes a while to go through the material, but it is well worth it. As a matter of fact, one of the best features is the tremendous volume of content.
Most exercise books have sections that say "pin", "discovered attack", etc. Chess Tutor(tm) has some of these, but mostly just "make the best move". This is the difference! The student must be able to evaluate the position, and discover what tactical possibilities lie within! You are not given any artificial cues, it's like being at the board against an opponent. Moreover, with a book, you either stare at small chess font or set up a board, which takes time. With ChessTutor(tm), there is a large format board already set up, waiting for you to make the right move!
The Chess Universities that are starting up now also offer position puzzles, and help solving them, but the feedback is often delayed until the followup lecture. With Chess Tutor(tm) the feedback is immediate, if you are right or wrong it tells you. Some of the lessons offer help and hint, but some don't. I like this better! It forces you to find the right move.
If you are already expert or better, maybe you don't need this product (or maybe you do!). But if you are less than expert, this product can definitely help. The only catch is that you must devote the time to go through the material. This product cannot be skimmed. It all builds very carefully on lesson after lesson, with all the exercises in between.