There are three games as of 2003:
Currently, the Escape Velocity games are only available for the Apple Macintosh. They support a large range of models. The first two are Classic-only, but Nova is Carbon, meaning it can run natively on both Mac OS X Classic and Mac OS X. At this time (2002) a port is underway to allow the application to be played by Microsoft Windows users by an outside company.
This series follows the general licensing rule for Ambrosia Software. All three games are shareware. Ambrosia's shareware system allows most distribution of the unregistered games. These copies will work without limitation for 30 days. After that period they will be hampered (in more ways in newer games) until the player buys a registration code which will unlock the entire game again. Ambrosia forbids distribution of registration codes.
The entire series features what most people consider a very open-ended plug-in architecture. This allows the scenarios to be completely rewritten or significantly added to by those in no way associated with ASW in terms of graphics, plotline, ships, missions, etc. This technology makes use of the Macintosh resource fork. Since Windows destroys any resource fork it sees, a conversion system is being devised in the porting process.
Most of the game takes place in a spaceship shown from third-person. There are various battles to be fought and places to go. The player can hyperspace between many systems. Many of these systems contain planets that can be landed on for various services like upgrading the ship with gadgets or even buying a new one. A mission computer and bar are one of the ways the plotline is advanced.
Many people consider this series unique in the way that it prescribes very little as to what the player can do. They can choose which missions to follow and which governments to form a good relationship with or to be entirely neutral. They can choose to be a trader or a mercenary or an asteroid miner among a number of things or a combination of several.
The three games are alike in gameplay only. Plot is completely different between the releases. Each release contains improvements on the previous engine.
EV Classic's plot involves the disputes between a Confederate government and Rebellion. As noted earlier the player can pick sides based on who they believe is right or who they believe is better off.
EV Override involves many more major governments, but the major conflicts are between the Federation and Vonians. The Vonians are much more easily seen as evil than either side in the previous game, but there is still a significant plotline should the player choose their side.
In EVN (also called EV3), there are six major governments, each with its own quirks. As always, the player is allowed to choose which to side with.