Open source is a set of principles and practices on how to write software. Literally "open source" means the source code is available to the users. There is a strong belief that one should not only get the source code but also have the right to use it. The movement was small until the big players got involved or supported the open source movement.
Fair Trade is similar to open source in sense that it is small and gaining traction slowly. Fair Trade needs the support of big players to bring about economies of scale and awareness to the general public. It is the masses that can take action. There is a strong belief that one should support fair wage and support producers throughout the world.
Great analogy! Fair trade is definitely picking up. A recent New York Times article "Fair Trade in Bloom" gives a sense of the growth.
"According to Fairtrade Labelling Organizations International, a group of fair trade certifiers, consumers spent approximately $2.2 billion on certified products in 2006, a 42 percent increase over the previous year, benefiting over seven million people in developing countries."