Citrix XenApp (formerly Citrix WinFrame Server, Citrix MetaFrame Server and Citrix Presentation Server) is a thin client product that allows users to connect to their corporate applications. XenApp can host applications on central servers and allow users to interact with them remotely or stream and deliver them to user devices for local execution
XenApp began life as an application hosting solution. Since 2007, XenApp has included application virtualization and streaming technologies that enable application delivery to user devices.
Unlike framebuffered protocols like VNC, ICA transmits high-level window display information, much like the X11 protocol, as opposed to purely graphical information. The Citrix Display Driver is installed in Session Space and captures high level GDI draw commands, which can be replayed on GDI-capable clients, for example Windows-based clients. Clients are available for several operating systems, including Microsoft Windows (CE, 16-bit, 32-bit and 64-bit platforms), Mac OS, Linux, and other Unix-like systems.
Citrix MetaFrame version 3.x and 4.x servers listen for client connections on TCP port 2598, by default. If the Session Reliability feature is disabled, then the server will listen on port 1494. Older MetaFrame servers (those running MetaFrame version 2.x or earlier) do not have the Session Reliability feature, and therefore always default to port 1494 remotely.
The Citrix Developer Network contains a set of software development kits that enable custom development for XenApp. These SDKs include the following:
- Citrix XenApp SDK
- Citrix Virtual Channel SDK
- Citrix ICA Client Object SDK
- Citrix Web Interface SDK
- Citrix Simulation API SDK
XenApp components, including application hosting servers, if any, reside on a Microsoft Windows computer, which can be either standalone or part of a larger cluster (farm) of Citrix servers. It is important to note that in addition to concurrent user Citrix licensing, there must exist a Terminal Server Client Access License (CAL) and a Windows Server CAL from Microsoft for each client connection. Both products must be adequately licensed for the environment to function correctly.
There is a web-based Citrix client, freely available under the name Web Interface for XenApp. The Web Interface client may be used as a secure ICA proxy over HTTPS when combined with Citrix Secure Gateway, both of which are included in the base XenApp product. XenApp also supports three UNIX variants: HP-UX, Solaris, and AIX which are included in Enterprise and Platinum editions of XenApp
Citrix XenApp competitors include Microsoft Terminal Services for Windows Server 2008, Quest Software vWorkspace, Systancia AppliDis Fusion, Spoon Server and Ericom Software WebConnect. XenApp is built on top of the Windows Terminal Server platform which was originally developed by Citrix in the early-mid 90s. Win4Lin Virtual Desktop Server provided similar functionality for serving Windows desktop sessions from Linux servers, while Sun’s application virtualization offering, the Sun Secure Global Desktop, serves to provide a complete solution allowing for the delivery of both Windows and Unix applications on all major platforms.Ulteo Open Virtual Desktop supports both Windows & Linux.