The developers over at REX Simulations have officially released REX SkyForce. The amount of features in SkyForce is pretty length and I could be here all day typing them. To name a few however:
3000+ Cloud Models/Structures (Based on real world cloud classification)
Integrated Flight Center
Innovative Sky and Sun Atmospherics
This and much more is all included in 4.6GB package that can be increased all the way up to 20GB. This is truly a competitor to active sky and I would be interested to see how it stacks up against it.