The reCAPTCHA 库让你可以为网站创建高级的CAPTCHA系统，这个系统其实是用来生成验证信息的，甚至包括语音验证，下图就是个好例子。
The reCAPTCHA library allows you to integrate an advanced CAPTCHA system on your website, which helps keep spam bots from posting on your website. The visual CAPTCHA also includes a helpful audio feature.In addition to the reCAPTCHA service, the library also includes an API for the "Mailhide" service which hides emails from spammers.The API is free and easy to implement on your site and also gives back to the community as it translates scanned books.
下载 ReCAPTCHA | 获得 API Key | 文档
Akismet is a free service that can be used on most small sites - or used on larger sites for a small fee. The library works by comparing comments to a database of existing spam comments provided by other users. The library can then decide to flag the comment for moderation or allow it through. Everyday the library grows and the service improves.
JSON is a handy format for transmitting human readable data. Not everyone has made the move to PHP5 which has included JSON support since version 5.2.0. This small library enables you to implement JSON functionality into your own applications if you are not using a recent version of PHP.
Smarty is a template engine which was formally a sub-project of the PHP project. Smarty provides many powerful features such as loops, variables, and a great caching system. The library has many years under its belt and is nearing its version three release.
下载 Smarty | 观看文档
In addition to displaying text data in your application, it can also be useful to show data in a more visual format. This can be done with a slew of options like pie charts and bar graphs. pChart is a script that allows you to create charts and graphs from SQL queries or manually provided details. The script is baked by GD to create the images. There is also a main focus on the aesthetics; so it creates some beautiful work.
下载 pChart | 查看文档| View Demos
SimplePie 让你轻松提取内容（好比RSS feeds)。它能和多种语言交互，也能处理各种格式的feed。
SimplePie allows you to easily pull in syndicated content (like RSS feeds). It's also been integrated with a lot of different platforms and language sets; it should be able to deal almost any feed in a variety of ways.
下载 SimplePie | 查看文档| 为独特的RSS Feeds拓展SimplePie
7. XML-RPC PHP Library
有时你需要使用XML-RPC技术去和其他网站交互，那么试试这个XML-RPC PHP 库吧。
Applications sometimes use functionality to "ping" other sites when an action has occurred (known as trackbacks). This is done by using a protocol called XML-RPC. The XML-RPC PHP library also allows you to integrate the functionality into your website.
下载 XML-RPC PHP | 查看文档
8. Amazon S3
Amazon有名的云计算平台叫做“S3”。这里就有Amazon S3 库 让你不用任何附加工具就可以使用云，上传大量数据文件。
Amazon provides a nice service to work in the cloud, called "S3". Nettuts+ even uses it to store the images seen in each article. There is a nice Amazon S3 library that doesn't require any third party tools and allows for large file uploads.
下载 Amazon S3 PHP Class
Most applications send out an email in some form, but usually rely on the basic php mail() function. PHPMailer is an existing powerful class that allows you to send different types of emails - from basic text to rich formatted emails. These emails can also include attachments or custom headers.
下载 PHPMailer | 查看文档