This site has a list of repos with fast growth in their number of stars: http://gittrends.io/#/explore?page=1&language=All&domain=All.... The list seems to be based on the shape of the curve of stars growth.

One of the problems I see with stars on github is the extreme hype around new JS frameworks, which is especially noticable in GitTrends. These projects are indeed trendy, but when you try to choose a tool / technology stars become problematic. I'm not saying that the metric I propose is more "objective" in any sense, but in my subjective opinion it promotes better values for open source projects.

Moreover, please don't think that I only count commits and see the about page (http://www.krihelinator.xyz/about) for more details about the metric.

Yes, I agree, but I also think the most interesting comparisons are intra-ecosystem. It does not make sense to use stars to compare a JS framework with a Clojure one, for example

Maybe an algorithm that ranks based on number of unique contributors in the past month or so?

I agree, that's why the number of contributors in the last week have the most weight in the metric. See the about page (http://krihelinator.xyz/about) for more details.

Yeah but Free Code Camp can't honestly be 'trending' for two years straight.

It does because one of the getting started tutorials features a GIF that suggests newcomers star their repository.