Created and tested by a multi-institution consortium with funding from the US National Science Foundation, this site offers Economics students "Math you need, when you need it." Each topic has explanatory text with examples, plus self-test questions and an instructor page with learning objectives and further links. The site has an online assessment tool, iMath, which course leaders can use to conduct online tests. There are five topics as of Summer 2014, with many more in development.
Online Text and Notes