FlightGear

Freeware

Freeware programs can be downloaded used free of charge and without any time limitations. Freeware products can be used free of charge for both personal and professional (commercial use).

Open Source

Open Source software is software with source code that anyone can inspect, modify or enhance. Programs released under this license can be used at no cost for both personal and commercial purposes. There are many different open source licenses but they all must comply with the Open Source Definition - in brief: the software can be freely used, modified and shared.

Free to Play

This license is commonly used for video games and it allows users to download and play the game for free. Basically, a product is offered Free to Play (Freemium) and the user can decide if he wants to pay the money (Premium) for additional features, services, virtual or physical goods that expand the functionality of the game. In some cases, ads may be show to the users.

Demo

Demo programs have a limited functionality for free, but charge for an advanced set of features or for the removal of advertisements from the program's interfaces. In some cases, all the functionality is disabled until the license is purchased. Demos are usually not time-limited (like Trial software) but the functionality is limited.

Trial

Trial software allows the user to evaluate the software for a limited amount of time. After that trial period (usually 15 to 90 days) the user can decide whether to buy the software or not. Even though, most trial software products are only time-limited some also have feature limitations.

Paid

Usually commercial software or games are produced for sale or to serve a commercial purpose.