Bitly
Distributed ID generation, edge-terminated redirects under 10ms, viral-link cache skew, and analytics that never touch the read path.
Dropbox
Content-defined chunking, global dedup with content-addressable storage, conflict resolution with vector clocks, resumable uploads, and folder renames that touch a million files.
Google Docs
OT versus CRDT, selective undo in a multi-user document, history compaction, presence at scale, offline divergence, and the room actor that owns a document.