Hello John,
It partly depends on what you mean when you ask "what's a cluster box."
Several have mentioned already that a launch system that has an igniter lead activated by a relay at the pad connected to a battery at the pad, can be used as a cluster box particularly when done with a quality clip-whip that you mentioned. The ways to build such a system have been endlessly and thoroughly discussed on this forum and I'd suggest doing a search for battery/relay at the pad launch system.
Certainly others use the old flash in the pad method for igniting clusters. It works fairly well in lighting the vast majority of very large clusters (like a dozen or more Estes motors), but usually there will be a couple of motors that do not light. I'm also guessing that you are looking for reliable and Flash-in-the-pan may not fit the bill.
But you did ask specifically about a cluster box, so I am going to assume that you want something to reliably ignite clusters of rocket motors. The usual low-power cluster is two or three Estes type motors which can usually be ignited off a single pad ignition system as long as you have a good battery, clean connections, and a good quality clip whip.
It ought to also be obvious that the more igniters you want to fire at once, the more thru-put in amps you are going to need. Having multiple relays or FETs operating off the same ignition switch might be very helpful along with having a battery that can put out enough juice all at the same time. You have not mentioned how large of a cluster you want to ignite. The more motors, the more difficult the simultaneous ignition from multiple relays or FETs will be.
If you want to ignite any composite motor clusters, you will need more than a PS2 for sure. And like Estes motors, the more igniters you want to ignite simultaneously, the more thru-put you re going to be need to be able to simultaneously engage.
If you are looking for a commercial system, I'm certain that there are several that would be possible. But of course one must ask if you need hardwired or wireless? If you are going hardwired, the possibilities are numerous. About any relay based system will work within its limitations. But if you need wireless, the reliable possibilities narrow down rather quickly as there are really only two reliable and legal to use wireless systems on the market: Telelaunch and Wilson F/X. You'll need to talk to Bdale about his system, but with Wilson F/X, I can build you any size cluster box that you want and can supply enough 12v battery power to operate all fired by a single-pad controller with all the igniter leads programmed to respond to that single pad-designation.
I did say "legal to use" because I've seen some folks using cheap chinese systems for low-power ignitions, that are not using legitimate frequencies allowed for rocketry here in the USA. Please don't go that route. You will regret it in the long run. I bought one for about $20 just to see what it was and how well it works. Frankly its a piece of cheap tech that is about as reliable as throwing matches from 20 feet away at a firecracker fuse. If you're lucky, you'll light the grass on fire and it will light the firecracker fuse for you.
Anyhow, there you have it. It really depends on the type of igniters you need to use and how many of them there are, and how far away you need to be, as to which launch sysetm is right for you.
Good luck.
Brad, the "Rocket Rev.," Wilson
Wilson F/X Digital Laundch Control Systems