Short but sweet. Intercom are masters of customer engagement, which makes sense since that's also the core of their product. You can get a lot of this content on the Intercom blog, but the book puts it neatly in one place. It's free too, which is always a plus.
The Intercom team offer practical how-to guides and check-lists for things like messaging, segmentation and onboarding. The focus on practicality is great and it provides a structure which makes the advice usable with a clear path to implementation.
Probably not one for the seasoned customer engagement professionals, but its a great overview. A must read for any company or employee who is starting to get to grips with customer engagement, particularly if you plan on using Intercom as your weapon of choice.