Design a video sharing platform like YouTube.

Design a POI (Point of Interest) system like Yelp.

Design a horizontal database sharding strategy covering shard key selection, data distribution, rebalancing, and failure handling.

Design a multi-tenant CI/CD workflow system triggered by git pushes, with job scheduling and a real-time progress UI.

Design a Slack-like real-time chat system with group chats, direct messages, notifications, rich media, and message deletion.