It is usefull also as an example to link a component to a database field.
 
Fully functional
Source: Included

• left mouse click for start date
• right mouse click for end date
• selection of a week by clicking on the week number (left click and then right click on week number or left click on one week number and right click on another week number)
• selection of a month by clicking on the month name
• selection of a year by clicking on the year number
• allow weeks to start on a Sunday or on a Monday
• allow the selection of the to date before the from date
• allow the same calendar component to be used to select a single date.

Features:

• Looks like TDateTimePicker, is rendered themed on XP
• can handle NULL values: shows empty field when not focused and date part placeholders (for example: __/__/__ ) when focused
• allows masked input (uses default mask, when no EditMask defined on the field)
• after completing one date part input (eg. day), caret goes to the next part (eg. month), ie. no need to type date separator characters
• clearing the field (with backspace or del) makes NULL value
• Drop-down calendar can show week numbers (like TMonthCalendar and unlike TDateTimePicker).

• Horizontal or vertical time axis
• Controllable active day start, active day end, day start, day end
• Events for insert, delete, left click, right click, moving, sizing of items
• Overlapped / non overlapped items
• HTML export, save to streams, XLS files, printing
• Built-in recurrency support
• Automatic code-less DB connectivity, samples for BDE, ADO, MS SQL, Interbase, etc
• Alarms, spell check support.
• Clipboard support
• Skinned or custom drawn items
• Much much more options
• VCL, VCL.NET and CLX version available.