  Soon after realizing that Cloud Computing could indeed help several
industries overcome classical product-centric approaches in favor of more
affordable service-oriented business models, we are witnessing the rise of a
new disruptive computing paradigm, namely Fog Computing. Essentially, Fog
Computing can be considered as an evolution of Cloud Computing, in the sense
that the former extends the latter to the edge of the network (that is, where
the connected devices -- the things -- are) without discontinuity, realizing
the so-called "cloud-to-thing continuum". Since its infancy, Fog Computing has
been considered as a necessity within several Internet of Things (IoT) domains
(one for all: Industrial IoT) and, more generally, wherever embedded artificial
intelligence and/or more advanced distributed capabilities were required. Fog
Computing cannot be considered only a fancy buzzword: according to separate,
authoritative analyses its global market will reach $18 billion by 2022, while
nearly 45% of the world's data will be moved to the network edge by 2025. In
this paper, we take stock of the situation, summarizing the most modern and
mature Fog Computing initiatives from standardization, commercial, and
open-source communities perspectives.
