```ruby
run lambda{|env| [200, {'Content-Type' => 'text/plain'}, ["heroku-modular"]]}
```

Use Rack::URLMap to run either FirstApp or SecondApp
user
```ruby
require 'first_app/app'
require 'second_app/app'

run Rack::URLMap.new(
  '/first_app' => FirstApp::App,
  '/second_app' => SecondApp::App
)
```
assistant