These grouplets have practically no budget, and they have no decision-making authority. What they have is a bunch of people who are committed to an idea and willing to work to convince the rest of the company to adopt it.
Consider the collection of engineers who wanted to promote “agile programming” inside the company. Agile programming is a product development approach that incorporates feedback early and often, and was being done in a few scattered parts of the organization.
The Agile grouplet formed to try to take this idea and spread it throughout the organization. It did so by banding together and reaching out to as many groups as it could to teach the new process. It created “Agile Office Hours” when you could stop by and ask questions about the process. It handed out books and gave internal talks on the topic. It attended staff meetings and created the concept of the “Agile Safari,” in which you could volunteer to work for a time in groups that were using Agile, to see how it ticks.