The new AppDisks feature separates applications and groups of applications from a master image’s OS, enabling you to manage them independently. You can now manage the applications as a distinct entity: an AppDisk.

AppDisks differ from other application-provisioning technologies in two ways: isolation and change management. Unlike Microsoft App-V, an AppDisk does not isolate applications; it separates them. Change management (updating master images and testing the compatibility of updates with installed applications) can be a significant expense to organizations. Using AppDNA with AppDisks provides this change management capability. AppDNA identifies potential issues with image updates and suggests remediation steps.

Enhanced support for Microsoft Application Virtualization (App-V)

You can now deliver Microsoft App-V applications to users without having to configure and manage Microsoft App-V management and publishing servers in Studio. Instead, you can import App-V packages directly from a network share to an Application Library held by Citrix Studio. App-V applications can be delivered through Delivery Groups to users from this library, just like other applications discovered from a master image or from Microsoft App-V servers, if you have them. The new "single admin" management method can be used instead of, or in addition to, the existing "dual admin" management method.

Applications node in Studio

The new Applications node in the Studio navigation pane provides a central way to manage all of your applications, regardless of Delivery Group assignment. One of its key benefits is the ability to add applications to more than one Delivery Group at one time.

In earlier releases, to manage applications, you selected a Delivery Group in the Studio navigation pane, and then selected the Applications tab in the middle pane. Now, you simply select Applications in the navigation pane.

When you add an application to more than one Delivery Group, you can specify the priority of each Delivery Group (0 is the highest); XenApp or XenDesktop will attempt to launch the application from the highest-priority Delivery Group; if that is not possible, the application in the second-highest Delivery Group will be launched, and so on.

The Add Application wizard offers a dropdown from which you select the source of applications: a machine created in the Machine Catalog, an App-V package, an application you have already added to the Site (perhaps in another Delivery Group), or a manually-defined application.

HDX technologies

• Framehawk support for HDX 3D Pro VDI. HDX 3D Pro support for the Framehawk virtual channel is extended from XenApp to XenDesktop VDI. This gives users greater flexibility to view large CAD models while on the move on a corporate or public wireless network, or working from an offshore location over a high latency connection.
• Framehawk server scalability improvements. Over 40% average reduction in memory footprint. Up to 20% increase in CPU efficiency.
• Framehawk touch scrolling improvements. Over 50% improvement in bandwidth efficiency when scrolling via touch input. Significantly increased frame rate resulting in a smoother user experience.
• GPU acceleration for DirectX windowed applications on Windows 10 VDAs. This release adds support for GPU acceleration for DirectX 10, 11 and 12 windowed applications on Windows 10 VDAs.
• Thinwire Build to lossless enhancements. The Build to lossless visual quality for Thinwire has been updated to sharpen fuzzy imagery at a faster rate than delivered in XenApp and XenDesktop 7.6 FP3, and to improve lossy or lossless frame detection.
• Reduced VDA memory footprint in Thinwire. The graphics encoder processing pipeline now eliminates the use of an intermediate frame buffer when running Thinwire without video codec compression.
• Clientname passthrough in double-hop sessions. Applications can use the updated WFAPI SDK to query the client endpoint name and pass this information from any Citrix Receiver to published desktops (XenApp/XenDesktop) and through to a XenApp application (a "double-hop"). This clientname awareness in the XenApp session means that users can seamlessly roam from location to location, and the "double-hop" application will be notified of the change in clientname without having to disconnect or reconnect the session.

• Session recording support from a Desktop OS VDA. Record on-screen activity of a user session hosted from a Desktop OS VDA over any type of connection, subject to corporate policy and regulatory compliance.
• Record sessions on remote PC. Support for recording sessions in Remote PC Access.
• Delivery Group rules.
• Keyword filtering during rule configuration.
• Special handling for unsupported graphics modes.
• Windows 10 support.
• Thinwire Compatibility Mode support.

Source: http://docs.citrix.com/en-us/xenapp-and-xendesktop/7-8/whats-new.html