Official Valve tools for map making and modding, which can be downloaded through the section of your Steam Library. 3. Troubleshooting Third-Party & "Repack" Launchers Left 4 Dead 2 - Authoring Tools - Valve Developer Community
Specifically for users installing the ray-tracing compatibility mod. L4D2-RTX on GitHub Authoring Tools: Left 4 Dead 2 Launcher Exe Download
An open-source tool that provides a GUI to manage VPK addons and launch options separately for L4D1 and L4D2 content. L4D Launcher on GitHub RTX Remix Launcher: Official Valve tools for map making and modding,
For most users, the "launcher" is simply the primary executable located in your game files. If this file is missing or corrupt, it prevents the game from starting via Steam. Official Location: Left 4 Dead 2 Launcher Exe Download