This is just one class (not perfect) that I develop for mine site. So I share with others.
What is purpose: checking password length
Based on: Brute force attack class A
How you get result :
-calculate entropia of characters used in password
-calculate same letters upper and lower case - lowering points
-calcuate different letter groups in row, upper\, lower, numbers and special characters.
Results: you can play with this class and as output password guessing time, etc.
Could be extended: yes I use for online password check in registration form with Ajax and live update whule user tyoe it.