Linux readdition of shared apps and Coherence-ish experience

We propose restoring support for shared Linux applications on macOS host systems, complete with desktop shortcuts, file type associations, and a FreeDesktop-compliant implementation including proper application subfolder organization. This feature requires minimal ongoing maintenance and delivers high utility, as the majority of users running Linux virtual machines via Parallels are software developers who would benefit greatly from native handling of Linux-associated file types on their host system. Following the existing implementation for Windows guest operating systems, bidirectional application synchronization with paired file associations could also be implemented with minimal development effort, a capability that has not previously been available for Linux guests.

For macOS guest virtual machines, one-way or bidirectional shared application integration could similarly be implemented with low maintenance overhead. At present, use cases for this functionality are more limited, though it may still merit development for future releases.

There is clear, well-demonstrated demand for full Coherence mode support for Linux guests. The existing seamless desktop integration functionality available for WSL2 and Crostini confirms strong user interest in this capability from macOS-based developers. Review of legacy guest tool ISOs indicates that prior implementations relied on a GNOME 3 extension, while even older builds from the GNOME 2 era used a separate, distinct integration method.

Two implementation paths are available. Approach A would adapt the legacy GNOME 2 Coherence shell to support the widely used MATE desktop environment, alongside full GNOME 3 compatible integration for the more popular Cinnamon desktop environment. Approach B would leverage Waypipe in combination with an open source macOS Wayland client such as Wawona, paired with X11 forwarding via XQuartz.

It should be noted that the Approach B implementation does not deliver true toggleable Coherence mode, as it requires users to launch an individual application to activate the integration. A hybrid implementation combining both approaches is also feasible: application forwarding functionality could be branded under a separate name such as Congruence, Convivencia, Crystal (a throwback), while users who require frequent full desktop switching would use the desktop environment-native integration path. Supplementary features including system tray icon support, and integration for default system applications for web browsing, communications, and email can be added in subsequent updates.

Coherence mode support should probably also be reinstated for future macOS 27 guest virtual machines. The upcoming discontinuation of Rosetta 2 in macOS 28 may likely drive a fast-growing cohort of users to purchase Parallels specifically to run older macOS releases that retain Rosetta 2 functionality. A recommended user experience improvement for this implementation is to automatically hide the guest macOS Dock, and integrate the guest application switcher into the secondary guest menu bar maybe via a third party application.

Poor adoption of prior Coherence mode implementations for Linux and macOS guests likely stems from two root causes. First, the features were never sufficiently promoted, leaving the vast majority of users unaware of their existence. Clear, prominent communication of Coherence support for Linux and macOS guests will resolve this awareness gap. Second, legacy implementations suffered from well-documented usability issues: redundant chrome such as duplicated Docks and menu bars for macOS guests, and equivalent redundant interface elements for Linux guests. This design produced a clunky, unpolished user experience even if the feature performed well technically.