The standard Humanscale keyboard tray has historically been the most popular system out of every brand that is available. It’s a combination of a quality product and really good marketing that make Humanscale the well-known brand that it is.
Just to reiterate, an adjustable keyboard tray is something that attaches to your computer desk (or whatever worksurface you use, not glass though) and allows you to place your keyboard and mouse on it to accomplish two main things: to reduce desktop clutter by freeing up a bunch of space, and most importantly allowing you to adjust the position of your keyboard and mouse for optimum ergonomic placement and enhanced comfort.
Many people develop various conditions and ailments after working on a computer every day for years on end. An ergonomic keyboard tray is important to help reduce the chance of developing such a condition and preventing the pain and strain most people are accustomed to feeling when working on the computer.
There are four main components to a Humanscale keyboard system: 1) The tray your keyboard goes on, 2) the tray your mouse goes on, 3) the arm, or mechanism, that attaches the keyboard & mouse trays to your worksurface allowing adjustment of both trays, and 4) the steel track that is mounted on the under-side of your worksurface and holds the arm/mechanism in place.
Humanscale offers a bunch of variations of each of the main components, so it is fairly easy to build your own keyboard tray system that will fit your specific situation perfectly – and they are simple to install as well.
The different keyboard platforms that Humanscale offers are: Standard (for regular keyboards), Curved (for ergonomic keyboards), Combo (can be used with standard or ergonomic keyboards), Big Board (a wider board that you place both the keyboard and mouse on, so there is no separate mouse tray), Radiused (has a curved edge to fit desks with a, you guessed it, curved edge), Extender board (for corner workstations where you need extra length to bring the tray out far enough), and Diagonal Big Board (same as regular Big Board but with cut corners), Goldtouch (specifically designed to fit the famous Goldtouch Split Keyboard).
The different mouse trays available are: Swivel (slides under keyboard tray if you take your mouse off), Clip (this one is cool, you can adjust the mouse platform into four different positions and also on the right or left side), and M2 (just like the Swivel but with a slightly larger mousing area).
The arms or mechanisms available are: 6G, 5G, 5GSM (same features as standard 5G but with a short mechanism for narrow work spaces), 4G (a step up from the 2G, but not as good as the 5G), 4GAD (same features as 4G but can be adjusted for use above the work surface), 2G (original arm that started it all), SM (short mechanism), AD (same features as 2G but for working above the worksurface), DS (double swivel provides additional pivot point), and KM (preset tilt and more knee clearance).