I built a real-time collaborative code editor (think Google Docs for code) in 6 weeks. Here's what I learned the hard way. The problem: building real-time sync sounds simple until two users edit the same line simultaneously. Naive "last write wins" causes one user's changes to silently vanish — the worst possible UX in a collaboration tool. Achieved stable multi-user sync with zero conflict data loss in testing across 10 concurrent users. The interesting decision: I implemented Operational Transformation (OT) lite — not the full Google Docs algorithm (that's 50,000 lines of engineering) but a simplified version that handles the most common conflict patterns: concurrent inserts at the same position and concurrent deletes of overlapping ranges. The key insight was that most real collaborative editing conflicts are positional, not semantic — if you correctly transform cursor positions after every remote operation, the document stays consistent. WebSocket room management was the other hard part — when a user disconnects mid-edit, you need to flush their pending operations before removing them from the room or their last keystrokes disappear. What I'd do differently: I'd use CRDTs (Conflict-free Replicated Data Types) instead of OT from the start. OT requires a central server to order operations; CRDTs are peer-to-peer and scale better. I only understood this after building the OT version. Full case study on my portfolio → my-portfolio-one-zeta-50.vercel.app