This app was mentioned in 1 comment, with an average of 4.00 upvotes
Lowly med student here but one of my cards attendings loves using QxMD's Calculate.
It has simple stuff that everyone's heard of/knows/at one point had to memorize like CHAD VASc, CURB 65, PSI, Well's, 4T score of HIT to more complex formulas like APACHE II, risk of dialysis after cardiac surgery, PCI mortality, risk of recurrence of kidney stones.
It's organized by specialty, user friendly, has a clean GUI, and very easy to use.