I have been using whatsapp-purple---a WhatsApp protocol implementation of libpurple [1] for some time now and it works really well.

That being said, accessing it from within a browser window has it's advantage. I currently have to install whatsapp-purple on all machines I use & syncronising chatlogs via Dropbox has it's challenges...

[1] https://github.com/davidgfnet/whatsapp-purple