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Advanced PHP Techniques
Tips and tricks in PHP programming
CodeIgniter Version 1.7.2 User's Guide
Old but gold. Some legacy web application might be still using 1.7.2 version of CodeIgniter. If that is the case, you'll find this PDF useful.
Couchbase is a NoSQL database. Great for stroring huge amounts of data that needs to be retrieved in high volume of requests.
A J2EE server that can be used to build scalable web applications
iPod Touch iOS4 User Guide
Third-generation iPod Touch user's manual
PDF version of jQuery API
Magento Design Guide
Design Guide for Magento
PayPal Sandbox User's Guide
Guide for using the PayPal Sandbox to test your application
GE Digital Camera Technical Specifications
Zend Framework Study Guide
Zend Framework is a very huge library. This guide will help you focus on the topic that you need to focus on.