Sky (the software, not me
) offers plenty of real photos, whereas Cellestial is very much in depth, but gives sometimes more, sometimes less sophisticated computer graphics only, but you can actually move through the galaxy, in 3D. Stellarium is a planetarium software that actually can be used to control real planetariums. It is quite charming (I have it installed), helps oyu to get a quick overview on what the sky is looking like tonight, and does not more and not less than what you expect to see when taking that 1 hour planetarium lecture for the public. Actual version is 0.9 (stable, never had a problem with it).
I find Sky very fascinating.