Skype





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+.

Pros:
standard de facto  for video chats
+ huge user base
+ video call ability

Cons:
- completely unreliable text message delivery
- slow, consume much ram
- Android version is even more pain in the ass, then Windows one. –°onstant freezes and crashes awaits you.

Download:

PC version:
http://www.skype.com/en/download-skype/skype-for-computer/

Android version:
https://play.google.com/store/apps/details?id=com.skype.raider