Perpetual Calendar from Vertex42 is an Excel spreadsheet that creates calendars for any year from 1900 to 9999, beginning with any month you like, holidays included. It's extremely easy to use: Simply enter the year, tweak any fields, and click Save or Print. It behaves like any Excel template.
Perpetual Calendar downloads as a compressed file but opens normally in Excel when extracted. The spreadsheet is clearly configured, with a large year display above a 12-month calendar. To the right is a list titled Events or Holidays; it included not only traditional holidays but also tax day and equinoxes and solstices. Fields titled Year, Month, and Start Date let us change the year and set when our calendar should start, which is great for tracking projects and other fixed time periods. Another field let us create a custom title. We typed in 2012 in the date field and received 2012's calendar, then we typed in 2112: So far, so good. We entered 3112 and sure enough, the spreadsheet displayed January 3112, though we think compatibility issues would start to show up in the next millennium. How about 9999? Yes, it even creates calendars for 9999, though surely Microsoft will have released a substantial update to Excel by then. The spreadsheet gave it up by the year 10000, but it makes up for it by going back in time to 1900. Clicking the Web link on the interface took us to Vertex42's page, which offered documentation, screenshots, and more. However, this spreadsheet is extremely easy to use.
You need to have Microsoft Excel to run Perpetual Calendar, though Vertex42 offers an OpenOffice version, too. This is a great little calendar spreadsheet; just the thing for planning, recordkeeping, research, and staying organized.