Browser detection and feature detection: a brief survey of libraries and techniques.
Modernizr
“Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user’s browser.”
Taking Advantage of HTML5 and CSS3 with Modernizr
has.js
has.js – “Pure feature detection library, a la carte style.”
Detector
Detector is a simple, PHP- and JavaScript-based browser- and feature-detection library that can adapt to new devices & browsers on its own without the need to pull from a central database of browser information.
Stack Overflow pages
Plenty of lively discussion — as usual — at Stack Overflow:
JavaScript: Detecting browser library function – does one exist?
JavaScript libraries to detect browser capabilities/plug-ins
Library to detect and parse browser information
Browser detection versus feature detection
How do I redirect my client to a different page according to their browser?
Need a good JS browser detection library but not JQuery
Further reading
Browser detection in JavaScript libraries