You've designed data-intensive systems.
Google Docs: Operational Transformation for conflict resolution. WebSockets for real-time. Operation log + snapshots for persistence.
Dropbox: Block-level storage and sync. Deduplication via content hashing. Conflict copies for binary files.
Web Crawler: URL frontier, politeness rules, distributed fetching, Bloom filters for dedup.
Next, you'll learn strategies for your mock interviews.