cloud9

1. go to "https://c9.io"
2. sign in or sign up if you don't have account here.
3. choose project to edit.
4. click "clone to edit"
5. click "start editing"
6. share link with your team mate.
7. change permission to read-write.
8. now the paticipient with write access can edit the file.

Now they can do concurrent edit on same file, but concurrent edit at same line is quite hard. ;)

run "npm test" on cloud9, need to install required package. after start editting Foresee project, type command below in "console input box" (at bottom of screen).

npm install mocha -g
npm install should -g
npm install coffee-script -g