Bukkit

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This file is zipped in a .zip file, use an archive extracting tool to open it. Inside you'll find NoLagg and NoLaggChunks. Chunks is a Spout-addon, so you need Spout for that one to work. It features network usage reduction for clients, improving things like block changes.

May or may not cause issues on 1.00 servers due to a nasty world reference when saving chunks...