Website (and Android/iOS application) CalcMoolator is a one-stop calculation shop featuring various calculators designed to help you with decisions ranging from renting vs buying, to paying off credit card debt, to deciding if you should switch jobs.
You'll find various task-oriented calculators like CalcMoolator provides all over, but CalcMoolator creates and rounds up a ton of helpful calculators in one place.
If you don't see yourself using the website, you may still be interested in the Android/iPhone/iPad versions, particularly for things like the tip calculator. (Though it's not like the respective app stores have any shortage of tip calculators.)
Either way CalcMoolator is a potentially useful site to check out if you're looking for a little help figuring out your finances.