...or: How I learned to stop worrying and love the framework.
Apps are one of the most gorgeous things introduced by Dancer 2. They allow developers to take very sexy design decisions and encourage modular developement, with a lot of reusable code released on CPAN to make people happy.
Apps are not something new in web frameworks (nothing is actually new in this world). Django, one of the most important Python frameworks, is based on them.
Apps are a really explicit concept in Django. Every time you start a project you must define apps, there's no other way to do it (as in Python zen).
Dancer2 is pure perl, so apps are a bit more subtle and if you come from Dancer1 you could miss them. There's no App->new, no creation moment, no actual ritual to conjure an app in this dimension.
How do you create an App?
Easy: every module has Import Dancer2 is an App.
Yes, I know, there's nothing simpler than importing a module and you cannot believe something so simple is so powerful but so it is. You import Dancer2 => you create an App.
Then the world of the modular design is open to you, you can start thinking clever about writing your webapp. You can help world to be a better place... well, a better place where write Dancer websites, at least.
Everything decided inside an App is just inside it and cannot leave it.
Let us thinking about a site where every navigation starting with /funnylayout need a particular layout. You could check all the routes but why? This is just a "module" of your webapp with a particular behaviour.
Create a packege with a geeky-but-professional name: package MySite::Funny
Make it an app (no chicken blood needed!): import Dancer2
Decide a common prefix for all your navigations: prefix => '/funnylayout'
Set the layout: set layout => 'funny'
That's all, monks!
Now write all the routes you want, knowing they will have the same behaviour. Knowing that if you move them to another site, they'll still have the same behaviour.
Why aren't you excited? Can't you understand? Well, let me speak a little more about Django and one of the most importand feature of it: Django Admin. It's a very fast way to have a backend for a site and let users manage their data.
Dancer's most similar thing is SimpleCRUD. It's just a Dancer Plugin and it does wonderful things but it has problems like HTML interfaces hardcoded in the subs and very little space for improvement.
What if someone start developing and app with all the code of SimpleCRUD in it, made cleaner by a complete use of Dancer2 framework, with templates, plugins and all that stuff? You would just import it to access all your ORM data. You would change it to rewrite its interface or change its flow. Sky would be the limit!
Understand this or go with the Wotan worshipper on the hill, barking to the moon.