OFTW and the effective giving movement are part of a larger school of thought known as "Effective Altruism." Effective Altruism is:
(i) the use of evidence and careful reasoning to work out how to maximize the good with a given amount of resources, and
(ii) the use of the findings from (i) to try to improve the world.
EA therefore comprises both donating and dedicating time to causes. It also covers lots of "cause areas", or areas in which research and resources should be allocated in order to maximize the good that can be achieved by its members. For more on other cause areas and ways to take action, we recommend visiting effectivealtruism.org
Within EA, global health and development is just one of several primary "cause areas". Other cause areas include animal welfare and long-term existential risk. The videos below are a good introduction to some of the key ideas in EA, as well as some of the key thought leaders.