UltraVNC Extend Display - UltraVNC VNC OFFICIAL SITE, Remote Desktop Free Opensource

UltraVNC Extend Display creates a genuine Windows virtual monitor on your desktop PC, extends the desktop onto it, and streams only the changed regions to a second PC over your local network. The second PC shows it full-screen, just like a physical extra monitor.

Key features

Real Windows monitor

Uses a signed IddCx virtual display driver, so Windows sees it as an actual display you can extend and arrange.

Auto discover & connect

Run the client with no arguments and it finds the server on the LAN and connects automatically. Manual discovery also connects on the first match.

Display-only client

The laptop does not send keyboard, mouse, or touch input back. It behaves as a monitor, not a remote-control session.

Auto-reconnect

Reconnects automatically after lock/unlock and network interruptions.

Efficient streaming

DXGI Desktop Duplication captures only changed rectangles and JPEG-encodes them, with adaptive quality pacing.

Runs as a service

The server installs as a Windows service and starts automatically, with no console window needed.

How it works

On the desktop PC, the signed UVncVirtualDisplay driver creates a real virtual monitor.
Windows extends the desktop onto that monitor.
The service captures only the changed regions, JPEG-encodes them, and streams them over TCP port 5950.
The laptop client listens for discovery beacons on UDP port 5951, connects automatically, and renders the stream full-screen.

Requirements

Windows 10 or Windows 11 on both PCs
Both PCs on the same local network
Administrator rights for the installer
Server component: 64-bit Windows 10 version 1903 (build 18362) or later
Client component: 32-bit or 64-bit Windows

Quick start

Desktop PC (the one being extended):

Download and run UltraVNC_Extend_Display_Setup.exe as Administrator.
Choose Server on the components page.
The installer installs the driver, registers the UVNCExtDisp service, opens firewall ports 5950/5951, and starts the service.

Laptop / spare PC (the extra screen):

Run the same installer and choose Client only.
Run ultravnc_extdisp.exe. The client automatically discovers the server and connects.
Press Escape to exit full-screen.

You can also start the client with a specific host: ultravnc_extdisp.exe <desktop-pc-name-or-ip> [port].

Support and documentation

Known limitations

LAN only; no NAT/Internet traversal yet.
The extra monitor is positioned to the right of existing displays.
When the desktop PC session is locked, the client display freezes; it resumes automatically on unlock.
Windows only for v1.