Pico is an open source CMS application that is capable of very few things. It uses flat-files as the database and built with PHP. Simply, there is no setup and the app works instantly.
phpFreeChat is a free and open source PHP chat application that doesn’t require any database to run but rather uses the filesystem for it.
phpFastCache is an open source PHP caching library that comes as a single-file and can be integrated so quickly.
Medoo is a lightweight (~8kb) PHP framework for working with SQL databases. The framework comes as a single file and works withВ MySQL, MSSQL, PostgreSQL,В SQLite (and more).
In order to manage MongoDB databases easily, Genghis, a single-file, self-hosted and web-based solution is pretty handy. It can be installed either as a Ruby gem or as a standalone PHP script.
Koken is a free and self-hosted CMS (PHP-MySQL) that is focused on building websites where portfolio/gallery is in the core (like designer or photographer sites).
BugKick is an open source bug tracking and task management application (source is hosted on GitHub) that is “light” in means of features (which i sometimes nice).
Mobile_Detect is an open source PHP class for detecting mobile devices.
The most standard way online for informing and guiding users to help them find the answers to their questions about the service/app are F.A.Q. pages.
Easily remove array of elements from another array.