Extension that does something like this:
def build(*) if settings.memcached? use Rack::Cache, :backend => :memcached use Rack::Session::Memcached # ... end super end
sinatra-smart-cache: update cache header only if arguments are more restrictive than curent value, set caching headers that way for most helper methods (i.e.
Some verbose logging extension: Log what filters, routes, error handlers, templates, and so on is used.
Form helpers, with forms as first class objects that accepts hashes or something, so the form meta data can also be used to expose a JSON API or similar, possibly defining routes (like "Sinatra's Hat"), strictly using the ActiveModel API.
sinatra-content-forto support Liquid, Radius, Markaby, Nokogiri and Builder. At least the first two probably involve patching Tilt.
Helpers for HTML escaping and such.