I can develop web applications for the GAE (Google App Engine) platform using both Python and Java languages. Front-end typically includes a Bootstrap+jquery sprinked with the awesomeness of Google Fonts and open source libraries like font-awesome!
For backend data storage, the most preferred service is firebase though you can have your own preferred choices too.
And needless to say, integration with other Google APIs like Drive, Calendar, etc. is also possible through Google's OAuth support. As for integration with third party APIs like PayPal, Dropbox, Shopify, etc., that is also included!