Thanks for specifying how you want answers delivered! This isn't about any one movement (it's a meta-answer), but I'll post it here because I think it points to action that you or someone else could take to resolve the question.
Rather than trying to think of all the movements/groups I can and filtering by "seems synergistic", I'll try to break this question down.
Any group with which we share some common trait might have synergy; the number of common traits should correlate with the level of synergy.
Some traits of EA:
- Cares about charity
- Cares about career choice
- Cares about using evidence
- Cares about maximizing output/ being efficient
- Cares about certain "neglected" groups: The global poor, farm/wild animals, people in the future
- Cosmopolitan, with a focus on the entire world/"grand strategy"
- Political lean toward economic conservatism and social liberalism
Charities themselves may not be huge fans of us if they see us as critical/rivals, but people trying to donate are synergistic with us. Which groups of people spend a lot of time trying to donate? People with a lot of money, people planning their legacies, people who work as charitable consultants, etc.
You can do the same thing for each list item, and try to notice which groups fall into multiple categories or have "anti-categories" they expressly don't fit:
- Many Buddhists care about the global poor, cosmopolitanism, and charity.
- Libertarians like efficiency, economic conservatism, and social liberalism.
- College students like social liberalism, career choice, and cosmopolitanism (but aren't big on economic conservatism). And so on.
If you do wind up building a list in this way, you should share it on the Forum more generally! I've wanted a resource like this for a while but haven't had time to build it carefully.