Special Features Available on Video Cards
Some video cards have special features that are only of interest to some people. At the time of this revision, the most popular special features include the following.
Real-Time Ray Tracing
"Ray tracing" is a graphics rendering technology that attempts to render effects from the perspective of a human eye, taking into account the ways the light will bounce around and interact with the various objects in the scene. It produces a more realistic rendering of things like shadows, reflection, refraction, and so forth. It produces more photorealistic images that can really make you believe the scene is real.
The problem is that it also requires enormous processing power and RAM, and because of that, tends to be slow. It works fine for things like most scenes in movies, which are relatively simple and slow-moving; but until recently, it was much too slow for games. But a new generation of video cards that support real-time ray tracing claim to be able to do ray tracing in real time, mainly by packing more processing power and RAM onto the cards than many computers contain.
In order for real-time ray tracing to actually do anything, the underlying software has to support it. It's expected that most or all high-end games will incorporate support for it within the next couple of years, and some already do. I suspect that professional-grade video-editing software and possibly some CAD software and 3D modeling software will also add support within a few years.
For anyone else, I think it's a very expensive luxury from which you may derive no benefit before the rest of your computer becomes obsolete. Unless you use applications like these that are likely to integrate support for real-time ray tracing within the next few years, maybe this is something you'll want to consider for your next computer-building project.
Video Cards with TV Tuners
Some video cards include television tuners that can be used to receive input in the form of a radio-frequency television signal from a television antenna or cable or satellite TV box, and display it on the computer's monitor or feed it into other video components. The software for most of these cards allows the television to be shown either in a small window ("picture-in-picture") or full-screen.
The ability to watch television on your computer is a popular feature among people who like to monitor the news while they work. It's also a handy feature for people who live in small apartments and want to save space by using their computers as televisions.
Video cards are also available with HD (High Definition) tuners built in, and the tuners also are available as separate cards (or USB/FireWire devices). These allow you to view HDTV on the computer's monitor, or sometimes to be connected to an external television set or satellite box.
Video Capture Cards
Video capture cards (or "vidcap cards") may be internal or external and allow whatever is being displayed on the screen to be recorded as a video file. They are popular mainly among gamers who want to share their games, and people who create instructional videos. More advanced ones are able to accept, mix, and edit multiple audio and video tracks (for example, a web cam feed of a player playing a game and the screen the player is seeing).
Dual-Monitor Video Cards
Many video cards are capable of driving two monitors and are called, appropriately enough, dual-monitor video cards. These cards are popular among both gamers and power users who need more screen real estate for the work they do. They're very popular among all kinds of people who do creative work. Just as one example, many people who edit videos for a living or as a serious hobby use one monitor to control their editing software, and another to show the results of their edits in full-screen mode.