Popular modern video and text messenger. Mainly i use it for video calls. If you need only text messaging ability i can recommend to you more stable and optimized applications, than Skype [of course they support Skype protocol]. Under Windows it is freeware Miranda NG (x64) and under Android it is paid IM Pro+.
+ standard de facto for video chats
+ huge user base
+ video call ability
- completely unreliable text message delivery
- slow, consume much ram
- Android version is even more pain in the ass, then Windows one. Сonstant freezes and crashes awaits you.