Astrolog is relatively unique in astrology software for the following reasons: (1) It's 100% freeware. :) (2) It runs on multiple platforms, such as DOS, Windows, Mac, and Unix. (3) The full source code is available. (4) Features are accessible from the command line and from shell scripts. (5) It offers many features not found in most other programs.

Screen shots:

• Standard wheel. (My natal chart, with attached info sidebar.)
• Bi-wheel. (My chart on inside. Current transits on outsite.)
• Quad-wheel. (From inside to out: My chart, alt.astrology's, our time-space midpoint, our composite.)
• Aspect/midpoint grid. (Aspects on one side of the diagonal, midpoints on the other.)
• Local horizon. (View of the sky at a particular time and location on Earth.)
• Solar system orbit. (Screen shot from the Windows version, showing orbit tracks.)
• Gauquelin sector wheel. (The 36 sectors, showing plus zones.)
• Astro-graph map. (Straight and wavy lines on a map of the world.)
• Graphic ephemeris. (Plot of position vs. time.)
• Dispositor graphs. (Planet A is in sign which planet B rules, which is in sign...)
• World globe. (Astrolog can do animations of charts, including a rotating globe.)
• Constellation globe. (The celestial sphere divided into the astronomical constellations.)
• Biorhythm. (I guess Astrolog is more than just an astrology program.)