HideIt!

Allows almost any program to be minimized to the system tray by right clicking its minimize button.

4t Tray Minimizer is a lightweight but powerful window manager, which helps you to free up space on the desktop and the taskbar via the following actions:

TrayIt! - minimize to the system icon tray any program (Outlook Express, Notepad, Word, Internet Explorer, Sunbird, Thunderbird, Opera, OpenOffice etc.) and get more room in the Taskbar!

PS Tray Factory allows you to take a full control over icons in the system tray area of the taskbar. With PS Tray Factory you can: hide icons from system tray into menu, change the order of icons in the system tray (sort tray), restore tray icons after Explorer.exe crash and use custom icons.

Endlessly minimizes all windows except the active one.

HideWin sits in the system tray and enables you to hide any top-level window with its popup tray menu or an ALT+letter hotkey that it assigns automatically. It appears to be abandonware, but it is only 13KB and still works.

Trayconizer allows you to minimize virtually any application to the system tray rather than having it take up valuable space in your taskbar. The screen shot to the left shows Trayconizer minimizing Notepad to the system tray.Using Trayconizer is simple. To start Trayconizer on Notepad, you would execute: C:\Path\To\Trayconizer.exe C:\Windows\Notepad.exe.