what do you mean by that? build your own indicator? do you mean mathematical construction of it? you can do it in excel, you know..not sure how free site(assuming you are talking about WEB site) fits in..
open office is good,but without understanding what exactly OP is asking for-it's all pointless. english is not my native language and i never attempted any college or whatever,but i think for this guy good starting point would be-learn how to build your questions right. cause for lousy asked question-you will get same vague answer.