Working on a manuscript simultaneously with your collaborators in Google doc is such a fun thing!
How about inserting references?
We usually download the manuscript into Word (*.doc) when it's nearly done and insert references in MS Word with external software such as Papers, EndNote etc. Most of the reference managers are not free. Now, this pain is over!
Solution: use Flow!
Flow supports to save the references from website to your Flow account and then from your Google doc Add-on, you can insert and format citations easily.
Here is the steps:
1. Set up a Flow account (you can also create a collection and share with your collaborator)
2. Import references from web sites (or other tools such as Mendeley etc.): http://help.flow.proquest.com/customer/portal/articles/1087119-save-articles-directly-from-the-web-using-save-to-flow
3. Install Google Add-on for Flow: https://chrome.google.com/webstore/detail/proquest-flow/oekoebnddahgfhaalgnopcfhofmgnekd