Intercom is one of my favorite tools. We've used it on Product Hunt for the past few years (it's the little icon bubble you see at the bottom right of the screen) to chat with the community and resolve support issues.
You can also program it to prompt specific people at specific moments in time. For example, if a user visits their shopping cart and fails to continue checking out after 10 seconds, you could send an automated message offering help. This type of feedback in the moment, can be very insightful.
