Citrix is the company that essentially invented modern day Microsoft Windows server-based computing. MetaFrame XP offers dozens of features, including the all-important application load-balancing, application publishing with seamless windows, and a web interface user portal.
In addition to the core features of MetaFrame, the license fee includes rights to use applications such as "Citrix Secure Gateway" (CSG). CSG lets you funnel all of your users, completely encrypted, through a single port on a single IP address. Think about it. With Citrix, you can provide secure remote access to thousands of remote users over a single IP address/port combination.
While not included with the core product, Citrix also offers a number additional products that further extend MetaFrame's capabilities. Example include MetaFrame Conferencing Manager (a product that enables real-time application sharing and collaboration between users anywhere in the world) and Meta-Frame Secure Access Manager (which provides secure and personalized information via a web portal).
The downside to Citrix is their price. While Citrix MetaFrame clearly offers the most features and capabilities, it is also the most expensive, with per-user MSRP prices starting at almost $100 more than the next most-expensive competitor.