Coda allows you to refer to collaborators directly in your doc or in comments. Simply insert the "@" sign and begin typing - you'll see that all the people you've shared the doc with are available to mention.
People in Tables
Coda also allows you to set the format of a column to People, which is great for assigning tasks and owners. This allows you to easily reference anyone who has access to the doc, and notify them when their name is added.
Whenever you reference a person - in a comment, in text, or in a table - that person will receive an email notification letting them know they have been mentioned in the doc so they can take action.
If you want to see a summary of your notifications, you can click the notifications panel in any of your docs. To resolve your notification, simply open the doc it's from.