An interesting attempt to categorize applications and suggest the appropriate structure of each.
A "holotype" is
a single type specimen upon which the description and name of a new species is based. - so they look at Facebook as an example of a "social network" holotype, and broadly describe the structure of the app.
An issue with it is that they neglect to consider scaling and organization structure - so if you're considering how to structure your application and it's broadly facebook-ish, you might want to do the same thing as them but you're operating under very different constraints!
Still, it's very helpful to look at what's been done in the past and consider how and where your application is actually different, so that you can make wise decisions and take risks in the appropriate places.
It's very frontend-focused, it would be interesting to try and consider backend holotypes.