ExternalSort is a class that can sort large files similar to the Unix sort command. It can read the file to be sorted in small buckets associated with temporary files to not exceed the configured PHP memory limits. The buckets are sorted individually and then merged to produce the final sorted output. The class provides command line interface options so it can be executed as a command from a shell.
RainCaptcha is a CAPTCHA class that does not require any image processing extensions (GD, ImageMagick, etc). CAPTCHA was developed to be readable by humans and resistant to OCR software. It generates black-and-white images with 5 distorted letters on them and noise. Its checking algorithm is case-insensitive.
Multi-Sandbox Lua Engine (MSLE) is a modified Lua interpreter which supports creation and maintenance of multiple "100% tight" sandboxes from within Lua. "100% tight" means that the amount of memory used by a sandbox (counting both code and data) is strictly limited, a feature Lua did not offer before.
PHP Debug is single API for tracing PHP applications. With a single file of only 200 lines, you can add, with minimal impact, diagnostics to be displayed upon program termination. Each diagnostic contains file, function, and caller function information. You just need to include the debug.php file and add debug() calls throughout your code in the same way as var_dump(). The diagnostic messages are stored and displayed in a list. Diagnostics can be disabled and controlled. It's small and simple yet very versatile.