Web Fundamentals (https://developers.google.com/web/fundamentals/):
- Service Workers: https://developers.google.com/web/fundamentals/getting-started/primers/service-workers
- Background Sync: https://developers.google.com/web/updates/2015/12/background-sync
- Web Push Notifications: https://developers.google.com/web/fundamentals/engage-and-retain/push-notifications/
- Web App Manifest: https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/
- Web App Performance: https://developers.google.com/web/fundamentals/performance/
- App Shell Model: https://developers.google.com/web/fundamentals/architecture/app-shell
Other Articles:
- Progressive Web Apps Checklist: https://developers.google.com/web/progressive-web-apps/checklist
- Progressive Web Apps: Escaping Tabs Without Losing Our Soul: https://infrequently.org/2015/06/progressive-apps-escaping-tabs-without-losing-our-soul/