[Looking for plugin] Live chat

Hi, I have check a lot of Live chat plugins, but I can not find the one that I need.

Can you guys help me with finding live chat (like support chats) plugin that does not requires any registration in any website and the visitors of my website could contact me through it when I am connected with my admin account. When I’m not connected to admin account it should display that the chat is offline.

It would be a huge favour to me if you could help! Thanks in advance.