Hey, it could be a bit off topic but since I am a member and I believe there will be some people who experienced this already I will ask it anyway.

Well, I basically need an application for my webpage, blog, fb page. An HTML5 chat application (not flash chat). I want to have the ability to change my chat room design, I need it to work on mobile phones and that chats transcript can be exported to html or excel. I did some research and found Rumbletalk, which seems decent. Have anyone used it? How it works? If not can you suggest me some other software or service which is good?

Thanks a lot!
Well I think that Rumbletalk is your best option. It offers amazing number of features, and ability to change the design as much as you want. It works amazing on phones, tablets as well. I think it is very worth trying it out
Let me know if you need something with this. I will do my very best to assist you!