Effective Altruism (EA) is a movement trying to invest time and money in causes that do the most possible good per unit investment. EA was at one point called optimal philanthropy.
The basic concept behind EA is that you would really struggle to donate 100 times more money or time to charity than you currently do but, spending a little time researching who to donate to could have an impact on roughly this order of magnitude. The same argument works for doing good with your career or volunteer hours.
The Effective Altruism movement also has its own forum, The EA Forum. It runs on the same software as LessWrong....