[Infra] [IT]What tools can we co-work on one document

Hi all,

Some time we several engineers need to work on one same document during the preparation phase. There are google doc [1] and qq doc [2] for word, excel and slides.

Are there any tools to work on markdown file jointly? If you have recommendation, please let me know.

Thanks in advance.

[1] http://docs.google.com/ [2] http://docs.qq.com/