AgentZero is a fast User-Agent parser built in PHP.
It doesn't match full UA strings or patterns, instead it extracts and categorises features from UA strings, so is faster, and can handle new UA strings or variations of common UA patterns.
Most User-Agent detection libraries rely on lists of regular expressions to match user agent string patterns and extract information. With lots of patterns you can do an ok job of getting this info, but it is not dynamic enough, which leads to minor variations or new UA strings not being captured, and they tend to be quite slow.
AgentZero is a simple string matching library that splits the user agent strings up into tokens to extract information from each part, leading to more complete information, more flexibility in capturing new user agent strings, and better performance.