config.ru

require "rdiscount"
require "sequel"
require "sinatra/base"
require "sqlite3"

module Blog
  Sequel.connect('sqlite://blog.db')

  class Post < Sequel::Model
    def markdown
      md = RDiscount.new(content)
      md.to_html
    end
  end

  class Server < Sinatra::Base
    attr_reader :posts

    get "/" do
      @posts = Post.all
      haml :home
    end

    post "/" do
      post = Post.new(params)
      post.save
      redirect "/"
    end
  end
end

run Blog::Server

Rakefile

require "sequel"
require "sqlite3"

task :default do
  DB=Sequel.sqlite('blog.db')
  DB.create_table? :posts do
    primary_key :id
    string      :title
    string      :category
    string      :content
  end
end