Not at all—there are many other free software licenses. We have an incomplete list. Any license that provides the user certain specific freedoms is a free software license.
It is recommended that you run the most current stable release. This can always be found at the Drupal Project page. However, if there are no compelling features in the latest version, a contrib module that is important to you isn’t ready or you don’t have time, there is no need to rush your upgrade as long as security updates are available for the version you are running.
Yes, you can use drush –
drush is a command line shell and Unix scripting interface for Drupal
Allow modules to interact with the Drupal core.
Drupal’s module system is based on the concept of “hooks”. A hook is a PHP function that is named foo_bar(), where “foo” is the name of the module (whose filename is thus foo.module) and “bar” is the name of the hook. Each hook has a defined set of parameters and a specified result type.
To extend Drupal, a module need simply implement a hook. When Drupal wishes to allow intervention from modules, it determines which modules implement a hook and calls that hook in all enabled modules that implement it.
Allow the use of different database servers using the same code base.
Drupal provides a slim database abstraction layer to provide developers with the ability to support multiple database servers easily. The intent of this layer is to preserve the syntax and power of SQL as much as possible, while letting Drupal control the pieces of queries that need to be written differently for different servers and provide basic security checks.
Most Drupal database queries are performed by a call to db_query() or db_query_range(). Module authors should also consider using pager_query() for queries that return results that need to be presented on multiple pages, and tablesort_sql() for generating appropriate queries for sortable tables.