Experienced web developers usually have a ready-to-use register/login code (from older projects) that they can reuse.
For newbies or any developer without such a starting point, this login script with PHP and MySQL can be handy.
It is simplistic, object-oriented and secure (bcrypt with blowfish and using the official PHP password hashing functions).
The files in the package are well-organized and only a single database table is used.
There are 4 versions that cover every need from simple to full-MVC-framework-like usage.
Most advanced version has all the features like login, register, forgot password, captcha support, edit account, account package, avatar and more.
Script is totally free and open source. Also, it is actively developed and well-documented.
Requirements: PHP 5.3.7+, MySQL 5.1+
DebugBar is a free and open source app that can integrate into any PHP project and collect + present profiling data.
It has no dependencies, supports Ajax requests and includes generic data collectors and collectors for well known libraries.
New collectors and views can be added with ease and it is possible to save/re-run previous requests.
CaseBox is an open source and PHP/MySQL-powered web application for storing + managing records, tasks and files.
It has a desktop-like interface where we can create an unlimited-level of directories and store stuff in the structure preferred.
Tasks with deadlines can be created, assigned to users and the progress can be tracked easily.
We can store the information of clients and any number of files there as well. The contents of the files are indexed so that locating a PDF/Word.. file with its contents is pretty quick.
The application is multi-user where each user can have custom permissions. And, it can be extended with plugins.
Requirements: PHP 5.4+, MySQL 5.5+, SOLR 4+
When it comes to blogging, WordPress and Drupal are the apps that everyone think of at the 1st place.
Besides their popularity, they can easily empower any level of complicated websites with the features offered.
Anchor CMS is again an open source CMS/blogging app (PHP-MySQL) but focuses on blogging, less features and simplicity.
It is easily themable and extensible, installed quickly and small in size.
The app accepts both Markdown and HTML when it comes to writing posts. Custom JS or CSS can be used per-post by simply drag ‘n’ dropping the files.
Anchor CMS is also very well-documented and multilingual (many language files exist already).
Requirements: PHP 5.3+, MySQL 5.1+
Munee is an all-in-one library that handles many things related to optimization and manipulation of website assets.
The library has a powerful caching feature that can cache resources in both server and client-side.
It integrates well with the PHP image manipulation library: Imagine for resizing or cropping images (and caching them afterwards).
Munee can automatically compile LESS, SCSS and CoffeeScript. And, it can combine CSS + JS files into a single request. Also, these CSS-JS files can be minified for a better performance.
This PHP library integrates to any code easily with less effort and it can be used with or without .htaccess (good for Windows users).
Requirements: PHP 5.3.1+