I recently came across this free Arabic Hijri calendar tool.
It provides the current Hijri and Gregorian date, Hijri/Gregorian date conversion, age calculation, and date-difference calculations. It also includes information and countdowns for Islamic occasions such as Ramadan, Eid, Arafah, and Ashura.

I’d be interested to hear what others think about the tools and usability. Feedback and suggestions are welcome.