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Trayconizer allows you to minimize virtually any application to the system tray rather than having it take up valuable space in your taskbar.
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Trayconizer requires no DLL's beyond the base Win32 API libraries and will not store any entries in your registry.
Installation and Use
Download ZIP file and extract the single executable file.
Using Trayconizer is simple. To start Trayconizer on Notepad, you would execute: C:\Path\To\Trayconizer.exe C:\Windows\Notepad.exe.
You can create a shortcut in your Startup group to execute Trayconizer on a program that you use frequently but want to keep tucked out of the way in the system tray when you're not using it. There is even an option for starting the application initially in the minimized state.
Tested with RegShot and found no registry entries.
Also, see DM2 (current version, as of this date 1.23.1), it has this functionality, along with other functionality, if you need iconizing AND other stuff.