I've built a native Pascal multiplayer net engine using Indy (called AIR).
It runs well but not perfect... there are alot of issues to deal with. It gets complicated really fast.

It features:
- List server for clients to find servers
- Passwords
- Admin password / remote server control
- Sync only changing objects
- Sync creation/deletion of obj
- Client resyncs questionable obj
- Client can control any object
- See users name on obj and camera position
- Server authority of game state (users cant cheat)
- Moderate Smoothing (its playable but you can feel the lag)
- Simple chat
- etc

Unsolved issues:
- Compression of packets
- Hacker prevention
- Perfect smoothing
- Lag Compensation
- Perfect Physics Prediction
- etc

Although I havent OpenSourced it yet, (not 100% sure I want to).
It would be really nice to have a community or a team working on a networked engine.

In any case we'll be releasing a test of Blocked PVP multiplayer, in the coming weeks.