General synonyms:
* Altruist: Someone who acts unselfishly for the benefit of others.
* Helper: Someone who assists others.
* Donator: Someone who gives something freely, especially time or money.
* Benefactor: Someone who gives money or other help to a person or cause.
* Philanthropist: Someone who seeks to promote the welfare of others, especially by donating money to good causes.
Synonyms for a specific task:
* Offer: To make a suggestion or proposal.
* Step up: To take on a responsibility or challenge.
* Contribute: To give something, such as time or effort, to a common cause.
* Assist: To help someone.
More informal synonyms:
* Pitch in: To help with a task or project.
* Lend a hand: To offer help.
* Chip in: To contribute to a common goal.
The best synonym to use depends on the specific situation and the intended meaning.