Advertisers, Wall Street traders, and anyone who's ever fought for a share of the Windows desktop knows that the most important real estate on the planet is the screen you're looking at right now. And like all real estate, while some is good, more is better. We can't all have the quad-screen-from-hell, but a lot of us do have laptops or TabletPCs sitting next to our main display, and this post is about putting those extra LCD screens to better use.

You probably encountered what happens next as soon as you stopped thinking about how neat it was to have two screens on your desk, and started getting into a good work groove. It happens to everyone. You're in the zone, operating in flow, the computer as a seamless extension of your mind, until... you reach for information on the other screen, and nothing happens. Stopped cold, you look down and realize that you're using the wrong keyboard and mouse to get that information. Your concentration's broken, and you find yourself wishing that you could seamlessly move your mouse pointer from this screen to that screen, just like a real multi-headed monitor setup.

Thankfully, Scoble's blog has given pointers to no fewer than four tools that do just that: ShareKMC, Synergy, MaxiVista, and an internal Microsoft tool that I'll call "MSTool"*. What follows is a personal review of these tools - for a different perspective, see Loren's comparisons of ShareKMC vs Synergy, and ShareKMC vs MaxiVista.

• ShareKMC: Probably the best known of the tools - use one keyboard and mouse to control two computers, hitting a key to flip focus between screens. ShareKMC emphasizes cut-and-paste functionality, and the latest release is significantly faster than earlier versions.
• MSTool: My first love. Same basic approach as ShareKMC, but feels easier to work with because (1) it's even faster, and (2) you just move the mouse cursor off screen to change focus. Unfortunately like any good research tool it's got some rough edges: cut-and-paste only works in one direction, there's no support for extended keyboard and mouse functionality, and once or twice a day it would just wedge solid on me.
• Synergy: Downloaded but not yet installed at the office - hey, it's Sunday! From the README and Loren's post it seems similar to the previous two, with the additional bonuses of cross-platform use and support for more than two screens, but some rough edges (e.g. limited cut-and-paste functionality).
• MaxiVista: The latest contender takes a fundamentally different approach - rather than letting the two computers run independently, it uses a fake VGA driver so that your laptop becomes in effect just an extra screen for your host PC. The multi-monitor support in Windows XP promptly kicks in, you can drag-and-drop windows between the two screens, and some apps get smarter (e.g. Powerpoint 2003 drives both displays, showing edit mode on the first screen and slideshow mode on the second). Despite having to ship display bits over the wire, it's respectably fast.

Summarizing:

Right now I'm very happy with MaxiVista. If for some reason I lost my wired connection I'd go back to ShareKMC, and if I got a second TabletPC I'd check out Synergy. As for MSTool, the flakiness and the loss of my mouse's back-button outweighs the extra smoothness, so don't give up on ShareKMC yet Loren!

*This is not its real name, but after the Sideshow affair I'm taking no chances - Sideshow was a widely-used internal tool that was yanked after someone leaked the code. I'll return to it in a future post on "peripheral awareness"

Update: See also Scott Hanselman's review of MaxiVista from last year, and Gizmodo's review after my original post. Oh, and after the demo ran out I bought the full version.

Update^2: MaxiVista v2.0 lets you flip between "laptop as second monitor" and "laptop as second computer". Oh, and performance has gone from "respectably fast" to "can't tell it's not a real screen". Highly recommended.