Here's a flexible, simple pop-up calendar written to work across browsers. It's fully commented and customisable for language, colours, date format and the week's start day. The pop-up displays a month at a time from a specified range of years. The optional year, month and day input determines the initial month displayed. Allows disabling of dates, date ranges and days of the week. This is ideal for combination with server-side technologies to produce a professional application.