Wildfire Games, an international group of volunteer game developers, has successfully applied to make 0 A.D. an associated project at an organization called Software in the Public Interest, Inc. (SPI).
SPI is a non-profit corporation based in the USA, that acts as a fiscal sponsor to many open source projects, including Debian, Drupal and LibreOffice. This means SPI can accept donations and hold funds for the development of these projects, sign contracts on behalf of the developers, provide legal advice when they might need it and more.
Importantly, if you live in the United States, you can donate to 0 A.D. through SPI and deduct it from your taxes. (Europeans can donate to SPI through a non-profit association based in Germany, named ffis e.V., which has partnered with SPI.)