Tcl/Tk is listed below by others, but it’s worth noting that both Richard Hipp (SQLite) and Antirez (redis) are (or were) very deeply involved with Tcl. I think

Tcl/Tk is listed below by others, but it’s worth noting that both Richard Hipp (SQLite) and Antirez (redis) are (or were) very deeply involved with Tcl. I think there maybe a positive feedback loop/environment wrt engineering discipline. It’s worth exploring. I also second the praise below of John Ousterhout’s (inventor of Tcl/Tk) book “A Philosophy of Software Design”.