Multi-Source Video Capture Cards for Unix?

An anonymous reader asks: "I'm curious as to what video capture cards are being used successfully by the linux user base. I need to capture screen shots from 4 video sources and collect the images in a manner that makes them easy to present in a web browser. A 4 input card would be nice! But I could always use a matrix switcher to grab frames from each source periodically. Matrix-Vision has a card - the mvDelta - that seems to work, but alas, they don't sell single units. What's out there? Who's using it? Any suggestions?"