In QuicklyChat, when you're available and receive a video chat, your client automatically answers it, and the video appears in an unobtrusive notification window in the corner of your screen. We think this better captures the dynamic of a coworker walking up to your desk and being in your peripheral vision.

Most other video chat clients pop up an answer dialog which steals focus, and makes your computer ring, and that immediately interrupts you from what you're doing, whereas when people walk up to your desk, they generally wait until you acknowledge, or use body language/visual cues to determine whether it's a good time to interrupt.