The donations advertised in the homepage goes to Manas. Manas currently doubles that income as stated in https://crystal-lang.org/2017/12/19/this-is-not-a-new-years-resolution.html .
Those allows Manas to allocate time from developers to invest in crystal. Although I might be de most visible Manas developer during the last months, other developers joins in scoped or sporadic efforts as well.
Those activities are not always visible. Sometimes is brainstorming, discussing ideas, preparing material, coding, experimenting, giving feedback, etc. Some of them are: waj, ggiraldez, mverzilli, and matiasgarciaisaia.