SmartSystemMenu extends system menu of all windows in the system. It appends next custom items to menu:
Allows almost any program to be minimized to the system tray by right clicking its minimize button.
Last update is from 2015 but the project has been forked: https://github.com/benbuck/rbtray
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!Discontinued
The official website is no longer available. Last version, 18.104.22.168, released on June 2008, can be still downloaded from Softpedia.
KDocker will help you dock any application into the system tray. This means you can dock Openoffice, xmms, Firefox, Thunderbird, anything!
Just point and click. Works for all NET WM compliant window managers - that includes KDE, GNOME, Xfce, Fluxbox and many more.
PowerMenu is a small application that some extra menu items to the windows control menu in addition to the standard "Close", "Maximize", etc options. The extra menus are: Priority, Always On Top, Transparency and Minimize To Tray.Discontinued
The app is no longer updated, but it can be still downloaded from the official website.
Minime is a tool that allows you to minimize applications to the system tray using a simple hotkey. What makes this tool somewhat unique is that it keeps your system tray clean by minimizing all applications into a single tray icon.This app doesn't have any features at the moment.Discontinued
Last Update: 2013-04-10. See https://sourceforge.net/projects/minime-tool/
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.
The official website is no longer available. Last version, 1.0, released on June 13th, 2008, can be still downloaded from Softpedia.