Fenstr

A lightweight tiling window manager for Windows that lets you snap windows into custom regions using mouse or keyboard.

Features

• Drag-snap: Drag a window to the edge of your screen to see a region overlay, then drop to snap
• Scroll to divide: Use the scroll wheel while dragging to split your monitor into 1-10 columns (or rows on portrait displays)
• Span regions: Hold Shift or right-click drag across multiple regions to create larger zones
• Keyboard placement mode: Press a hotkey (default: Win+Ctrl+Space) to enter placement mode, then type a letter to snap the active window
• Win+Arrow shortcuts: Move windows between regions with Win+Left/Right
• Runs in the tray: Fenstr lives in the system tray with a minimal icon

Fenstr automatically disables Windows 11's built-in Snap Layouts to avoid conflicts, and restores them when it exits.

Install

Installer (recommended)

Download Fenstr-vX.Y.Z-setup.exe from the Releases page and run it. The installer places Fenstr in Program Files\Fenstr, which is required for hooking elevated windows (Task Manager, etc.). An optional "Run at login" checkbox registers Fenstr as a startup app.

Portable

Download the .zip from the Releases page, extract, and run Fenstr.exe. Note: hooks over elevated windows won't work from arbitrary directories (see Working with elevated windows below).

Both downloads are self-contained; no separate .NET or Windows App SDK install needed.

Build from source

Requires Windows 10 1903+ (Windows 11 recommended) and the .NET 9 SDK.

git clone https://github.com/patrickiel/Fenstr.git
cd Fenstr
dotnet restore
dotnet build -c Release

To publish a self-contained executable (no runtime install required):

dotnet publish -c Release -r win-x64 --self-contained

Replace win-x64 with win-x86 or win-arm64 for other architectures. The output will be in bin/Release/net9.0-windows10.0.19041.0/win-x64/publish/.

Working with elevated windows (Thunderbird, Task Manager, …)

Edge-drag snapping works for every window. But the mid-drag gestures (right-click to start a span, Shift to span, mouse wheel to change divisions) rely on low-level mouse/keyboard hooks, and Windows UIPI blocks those hooks over elevated windows (Task Manager always, Thunderbird if it was launched as admin). The overlay simply never appears.

The fix is uiAccess="true" in app.manifest (already set). Windows only honors it when the executable is signed by a trusted cert and launched from a protected directory (%ProgramFiles% or %SystemRoot%\System32). If either is missing, Windows silently drops uiAccess and the hooks stay blocked over elevated windows.

One-time dev setup

Create a self-signed code-signing cert and trust it on this machine (elevated PowerShell):

$cert = New-SelfSignedCertificate -Subject "CN=Fenstr Dev" -Type CodeSigningCert `
  -CertStoreLocation Cert:\CurrentUser\My -KeyUsage DigitalSignature -KeyExportPolicy Exportable
$pwd = ConvertTo-SecureString -String "temp" -Force -AsPlainText
Export-PfxCertificate -Cert $cert -FilePath fenstr-dev.pfx -Password $pwd
Import-PfxCertificate -FilePath fenstr-dev.pfx -CertStoreLocation Cert:\LocalMachine\Root -Password $pwd
Import-PfxCertificate -FilePath fenstr-dev.pfx -CertStoreLocation Cert:\LocalMachine\TrustedPublisher -Password $pwd

Place fenstr-dev.pfx in the repository root. It's in .gitignore. The cert expires after 1 year; regenerate when needed.

Build + deploy

From an elevated terminal (writes to Program Files):

dotnet build Fenstr.csproj -c Release -p:Platform=x64 -p:RuntimeIdentifier=win-x64 -p:DeployFenstr=true

This signs Fenstr.exe (via signtool from the Windows SDK) and xcopies the output to C:\Program Files\Fenstr\. Launch C:\Program Files\Fenstr\Fenstr.exe.

Override paths if needed with -p:FenstrSignPfx=..., -p:FenstrSignPassword=..., -p:FenstrDeployDir=....

Notes

• Release builds are self-contained (WindowsAppSDKSelfContained=true). A uiAccess process can't resolve the user's per-user Windows App SDK package registration and crashes on startup without the runtime bundled. Output is ~200 MB for that reason.
• To verify uiAccess is active: in Process Explorer, Fenstr's Security tab shows UIAccess: True. Simpler check: right-click or Shift during a drag of a Task Manager window shows the zone overlay.
• Debug builds use app.Debug.manifest with uiAccess="false" and therefore cannot interact with elevated windows. This is required because VS F5 activation of a packaged uiAccess="true" app fails with "The request is not supported" (the dev cert isn't trusted and the app isn't in Program Files). That's fine for most dev iteration; only test this feature against a Release deploy. Keep app.Debug.manifest in sync with app.manifest (they differ only in the uiAccess attribute).

Configuration

Settings are accessible from the tray icon menu. Configuration is stored in %AppData%\Fenstr\config.json.

Setting	Description
Run at login	Start Fenstr automatically when you sign in
Placement mode hotkey	The keyboard shortcut to enter placement mode (default: Win+Ctrl+Space)
Per-monitor divisions	Number of snap regions per display (1-10), adjustable via scroll wheel during drag
Region hotkeys	Assign keys (A-Z, 0-9, F1-F12) to specific regions for keyboard placement

Usage tips

• During a drag, scroll the mouse wheel to change how many regions the monitor is divided into
• Right-click drag (or Shift+drag) across region boundaries to span multiple regions
• In placement mode, press multiple letters quickly to snap a window across those combined regions
• Press Delete while hovering over a region in placement mode to clear its hotkey assignment
• Press Escape to cancel placement mode

License

MIT