```ruby
cask :v1 => 'omnigraffle' do
  version :latest
  sha256 :no_check

  url 'https://www.omnigroup.com/download/latest/omnigraffle'
  homepage 'http://www.omnigroup.com/products/omnigraffle'
  license :unknown    # todo: change license and remove this comment; ':unknown' is a machine-generated placeholder

  app 'OmniGraffle.app'

  zap :delete => '~/Library/Application Support/The Omni Group/OmniGraffle'
end
```

Add older versions of Omnigraffle for older OSX
user
```ruby
cask :v1 => 'omnigraffle' do
  if MacOS.release <= :snow_leopard
    version '5.4.4'
    sha256 '7bcc64093f46bd4808b1a4cb86cf90c0380a5c5ffffd55ce8f742712818558df'
    url "http://www.omnigroup.com/ftp1/pub/software/MacOSX/10.6/OmniGraffle-#{version}.dmg"
  elsif MacOS.release <= :mavericks
    version '6.0.5'
    sha256 'a2eff19909d1ba38a4f01b2beecbde2f31f4af43d30e06d2c6921ae8880f85bc'
    url "http://www.omnigroup.com/ftp1/pub/software/MacOSX/10.8/OmniGraffle-#{version}.dmg"
  else
    version :latest
    sha256 :no_check
    url 'https://www.omnigroup.com/download/latest/omnigraffle'
  end

  homepage 'http://www.omnigroup.com/products/omnigraffle'
  license :commercial

  app 'OmniGraffle.app'

  zap :delete => '~/Library/Application Support/The Omni Group/OmniGraffle'
end
```
assistant