If you want to have a group of actual friends that you communicate with, another solution has just gone multiplatform. There are other solutions already, such as Telegram and Cryptocat.

What is BitTorrent Bleep?

Peer to peer encrypted messaging. No servers are in between to store your messages, photos, videos, etc. Instead, you can send to each of your friends with a public key and they send to you with yours.

In addition, the company just added a Whisper feature so you can specify some messages to only last on your devices for a limited number of seconds before removal.

Check it out at:
http://www.bleep.pm/

Why use it?

Why not? There is no reason for your personal conversations to be stored for future reference by anyone including yourself (if you want).