As current maintainer of Sinatra, Konstantin is an Open Source developer by heart. Ruby has become his language of choice since 2005. He regularly contributes to different widespread projects, like Rubinius, Rack, Travis CI, Rails and Ruby.
"When I started reading it was clear that this book was worth every single cent...Not even a sentence is redundant in this excellent manual, surely it is a reference book to keep on hand."
--Alessio Caiazza, Abisso Dev.