NexKVM

Share one mouse & keyboard across two Windows PCs over your local network.
No hardware KVM, no cables — just slide your pointer off the screen edge onto the other machine.

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NexKVM turns a second Windows machine into a virtual extra monitor for your mouse and keyboard. Push the pointer past one screen edge and it appears on the other computer; your keyboard follows it, and the clipboard (text) stays in sync. It's built for speed — native input hooks, direct SendInput injection, and TCP with Nagle disabled — so on a normal LAN the added lag is about a millisecond and it feels like one continuous desktop.

Think Synergy / Mouse Without Borders — but a single, tiny, no-install app.

Features

• 🖱️ Seamless edge crossing — the cursor slides in from the far edge of the other screen; pick which side (left/right) the other machine is on.
• ⌨️ Full keyboard follow — every key goes to whichever screen the cursor is on (forwarded by scan code, so layouts and modifiers work correctly).
• 📋 Clipboard sync — copy text on one machine, paste on the other.
• ⚡ Low latency — designed so movement feels natural with no perceptible lag on a LAN.
• 🖥️ Simple GUI — pick a role, press Start. No command line.
• 🛟 Failsafe — Ctrl+Alt+F12 instantly returns control to the host, and control auto-returns if the network drops, so you can never get stuck.
• 📦 No install — one self-contained .exe. Download, run, done. (.NET is bundled inside.)

Roles

Both machines run the same NexKVM.exe. You just choose a role on each:

Role	Runs on	What it does
Host	the PC whose mouse/keyboard you want to share	captures input and sends it
Receiver	the other PC/laptop being controlled	receives input and applies it

Any PC can be the host and any PC can be the receiver — nothing is tied to a specific machine.

Quick start

1. Download NexKVM.exe from the Releases page and copy it to both computers (put it anywhere, e.g. the Desktop).

2. On the machine being controlled (the receiver — e.g. your laptop):

   • Run NexKVM.exe.
   • Choose “This PC is controlled (Receiver)”.
   • Note the IP address it shows (e.g. 192.168.1.50) — you'll need it on the host. Click Copy if handy.
   • Press Start. It now says “Listening for host…”.
   • If Windows shows a firewall prompt, allow it on Private networks.

3. On the machine with the mouse/keyboard (the host — e.g. your desktop):

   • Run NexKVM.exe.
   • Choose “This PC controls (Host)”.
   • Enter the receiver's IP address.
   • Set “Receiver is on my … side” to match where that machine physically sits (Left or Right).
   • Press Start. It should say “Connected”.

4. Use it: push your mouse off the chosen edge of the host screen → it appears on the receiver. Type anywhere; keys go where the cursor is. Push back off the opposite edge to return.

Failsafe: if the pointer ever gets stuck on the other machine, press Ctrl+Alt+F12 on the host to snap control back.

Do I need Administrator?

Usually no. You only need to run both apps as Administrator if you want to control elevated windows on the receiver (UAC dialogs, Task Manager, etc.). For normal desktop use, just double-click it.

Networking notes

• Both machines must be on the same local network (same Wi-Fi/router, or wired).
• Default port is 24800 (change it in the UI on both sides if needed — they must match).
• First run on the receiver may trigger a Windows Firewall prompt — allow Private networks. To add the rule manually (elevated PowerShell):

  New-NetFirewallRule -DisplayName "NexKVM" -Direction Inbound -Protocol TCP -LocalPort 24800 -Action Allow -Profile Private

• Traffic is unencrypted — intended for a trusted home/office LAN. Don't forward the port to the internet.

Building from source

Requires the .NET 8 SDK.

# Run/develop
dotnet run

# Produce the release single-file exe (lands in ./publish/NexKVM.exe)
powershell -ExecutionPolicy Bypass -File build-release.ps1

The build script publishes a compressed, self-contained, single-file win-x64 executable and zips it for release.

How it works

Concern	Approach
Capture (host)	WH_MOUSE_LL + WH_KEYBOARD_LL low-level hooks on a dedicated high-priority thread
Edge crossing	While away, the host re-parks the cursor at screen centre each move and drives a virtual cursor inside the receiver's resolution; a warp-race guard prevents mid-screen jumps
No drift	The host sends absolute normalised positions (0–65535), not raw deltas
Hidden cursor	The host swaps all system cursors for a blank one while controlling the receiver, so no stray pointer is left on the host screen
Inject (receiver)	SendInput with scan codes and absolute coordinates
Transport	One TCP socket, NoDelay = true, length-prefixed binary frames
Safety	Held keys/buttons are released on hand-back; Ctrl+Alt+F12 and disconnect auto-revert

Limitations

• Windows ↔ Windows only for now (macOS/Linux receivers would need a different injection backend).
• Clipboard sync is text only (no images or files).
• The host uses its primary monitor's edge as the crossing point.
• Not encrypted — use on a trusted LAN.

License

MIT