Interesting anecdote about FastMail, I was previously C++ dev lead at a company with a large (1~2 mloc) legacy code base. Most of the C++ code was layers of mess but there was also a very well engineered core. One name consistently appeared in comments on these well engineered sections. Out of curiosity one day I decided to search LinkedIn and see if I could find the guy behind this shining light of engineering competence. Turns out he went on to found (/cofound -- not particularly sure of the details) Fastmail.

I find it very satisfying that a good engineer went on to succeed and would definitely trust the engineering competence of Fastmail.