I need lightest simplest windows tool like combination of notepad and calender in a fashion of sticky notes , and want to keep always open but should have minimize button.
Easy Notes has these features and a bit more. It sits in the tray and has an easily accessible sticky-note interface as well as a calendar:
You can even put notes inside the calendar:
Easy Notes has a freeware "lite" version as well as a paid version available.
Rainlendar: highly customizable, skins, multiple calendars, to do list, alarms, recurrence, scripting, backup, printing, search, platform independent, localized, import and export, standards-compatible (iCal).
Pro only: Google Calendar support, Remember The Milk support, shared calendars, Outlook support.