1. Compatible with versions 4 and 5 of PHP
2. MVC architecture
3. Built-in validations
by default it is database.php.default, you can find it in /app/config/database.php.default
for connecting to database, it should be renamed to database.php
A controller is used to manage the logic for a part of your application. Most commonly, controllers are used to manage the logic for a single model. Controllers can include any number of methods which are usually referred to as actions. Actions are controller methods used to display views. An action is a single method of a controller.
bootstrap.php , yes it can be changed , either through index.php , or through htaccess