I have modified the TNT mod included with the default game to be safe for multiplayer games (To be fair, I've added about 3 lines). In my mod, TNT does not explode under any circumstances when placed above -100, so it can be used in deep mines without having to worry about griefing. It is deliberately named the same as the default mod, since this mod replaces it. It is used exactly the same way as the default mod.
Edit: When you light the gunpowder, there is an air-raid alarm to warn other players.
Browse the code, Download a .zip.