4.19 MHz is the clock frequency of the Z80A CPU, working in the Amstrad PCW (Schneider Joyce in Germany), one of the coolest electric devices ever built by humans. I grew up with this machine since the age of 5 and learned to understand and program computers with it. The Z80 also worked in the original Nintendo Gameboy which I owned since I was 7 or 8. In a sense, my whole life is heavily influenced by 4 MHz. (Sure, there were also other factors in my life that formed my character. We got a Super Nintendo later on.)
By and by, I want to present the software I write on this site. There's not that much available yet, but someday I'll have more time, and then... ;)