Planetary Aspects and Transits: A Tool for Users of Archetypal Astrology
If your idea of astrology is asking being concerned that your daily horoscope said "There may be difficulty ahead, but focus will prevail," using Planetary Aspects and Transits ($30, 20-day free trial) may require a bit of research. PAT doesn't use the zodiac, but instead focuses intently on the planets' orbits and their relationships, reporting on such intriguing-sounding things as "quincunxes" and "semisextiles."
What Planetary Aspects and Transits gives you is excruciatingly detailed reports on the relative positions of the planets on a given date, based on the idea of a geocentric (Earth-centered) model, and any patterns formed by these relationships. What it does not give you is any kind of "Today is a good day to ask for a promotion at work" readout. It is up to the user to apply the data, and this requires a good knowledge of "Archetypal Astrology." Archetypal Astrology ignores constellations (the "star signs") and relies on extremely precise calculations of planetary positions at a given instant, without dividing the year up into large blocks of time that were a consequence of the imprecision and limitations of ancient astronomy. (PCWorld, and this reviewer, make no statement on the value of this style of astrology vs. other styles, or of the value of astrology in general.)
The demo version of Planetary Aspects and Transits is rather limited. It applies only to dates prior to 1960, making it less useful for many people interested in their birthdates. If you're interested in testing the predictions of the model, you can enter historical dates and see if the results line up...but even this is limited to 20 days.
If you are familiar with archetypal astrology but don't want to do all the math by hand, Planetary Aspects and Transits may well be the tool for you. If you're looking for more "traditional" astrology or just a program to tell you if you'll meet a handsome stranger, it may not be of great use.