I've been torrenting for over 2 years now. I've been on many private torrent sites. Some of them use Custom tracking system/Codebased; Some of them (new trackers mostly) uses new UNIT3D tracking system, Others uses Gazzel, U-232, xbtit & few others I'm not trying to mention...
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But from my experience, Most of the Chinese tracker; At least those I've seen, Uses NexusPHP tracking system.
Here is my question, Why only Chinese site owners (or the trackers from Chinese country) uses NexusPHP?
Why it's so famous among them?
Because, At the moment; In term of features, functionality, security & support there are so many new tracking system availabe to choose from.