[tsm]

The two best:

1) Working (professionally) on a project that happens to be open source: https://github.com/metabase/metabase/

2) Coming to a Rails project mostly written by a very senior 7-person team. There was still a fair amount of jank (mostly from seed-round assumptions that weren't holding up when I joined after the Series A) but it still followed The Rails Way and nothing was too gross. It also helped that everyone important was still at the company and available for questions.

PS on (2): Seven of those original eight dev are now gone, including me; the median years of experience has gone from 8-10 to 0-3; the team size is at least 40 and I think more; and my understanding from friends still at the company is that the codebase is in general a flaming mess.