The Lastolite Tri-Flash is a bracket designed to mount 3 hotshoe flashes (speedlites) onto one lightstand. Tripling your flash is really useful when you want to get extra power, or combining low powered output for faster flash recycle times. The bracket also has an umbrella holder which can be used for shoot-through or reflective brollies. I always use an umbrella to diffuse the triflash otherwise there can be problems with multiple shadows.
There are 4 versions of the triflash. The standard model (pictured above) is the one I own. The Triflash Shoe-Lock has screw locks for each hotshoe, but all my flashes have their own hotshoe lock. The Triflash Sync has a built in sync system, but all my flashes are wirelessly linked to my transmitter. Lastly the Joe McNally Triflash has rotating hotshoes, but all my flashes have tilt/rotate heads anyway so again this extra feature is redundant. If you use any of the canon ex speedlites or nikon sb-xxx speedlights with wireless triggers I’d recommend just getting the basic Triflash.
The one criticism I have of the triflash is that you can’t use it with a softbox, however lastolite have since introduced the quad bracket and ezybox. The triflash has become an essential part of my outdoor lighting kit. Whenever I’m competing with ambient light I find the extra power useful, and even if light isn’t as much of an issue the faster recycling makes shooting much easier.