Workaway platform has thousands of work-exchange offerings around the world and is one of the most used among backpackers. In this site you can have access to all offers for free, however to get in touch with people it is necessary to create an account / profile and pay a fee of 32 € for a year.
It was through this platform that I got a two week job in Vietnam.
How it works?
First we need to create a personal profile with some information about us and our interests and availability. After reviewing the projects and feedback from other travelers we have contacted to see if they are interested in our help and to set the arrival and departure dates. As I mentioned, as it is a voluntary work there is no remuneration but in exchange for our work we receive accommodation and meals (these conditions change according to the proposal).