TKWeek

Need to convert between a week number and a date? With this app you can.  Want some information about a date, find out if a year is a leap year, calculate the number of days, working days (business days), weeks, months and years between two dates and add or subtract days, weeks or months to a given date? With TKWeek, it‘s no hassle.

TKWeek also maintains a list of annual and fixed events. You can add your personal events. Additionally, TKWeek displays the birthday and anniversary(s) of your Google Contacts.

TKWeek has several international public holidays built in. So, you want to know when Easter takes place? This app will tell you. Other special days TKWeek is aware of: Valentine's Day, Mother's Day, Halloween, Memorial Day, Thanksgiving, All Saints, ...

Do you want to know when Friday 13th takes place? This app will tell you.

TKWeek also offers a bunch of widgets.
Week info shows you the current week number, the total number of weeks in a year, the first and last day of a week and the current date.
Events shows the next event.  
Current Date is a simple widget that displays the current day of the week, date and month.
Day of year shows the current day of the year (julian date) and the total number of days in a year