Carrotmob gave me a crash course in startup life: even as an intern I worked on core features like analytics, polishing my skills to a professional level.
In a boycott, consumers punish a business that does something bad, but in a carrotmob, consumers can reward a business for doing something good. In exchange for something good, like putting in composting bins, consumers will "mob" that store, spending money. Carrotmob eventually pivoted, turning into The Spring, wherein a percentage of purchases at participating business would automatically go toward community projects.
The code for Carrotmob was written in PHP; The Spring was written in Ruby on Rails. This job provided me a solid foundation in those languages as well as introducing me to the fundamentals of source control.