I shipped BBS doors at thirteen. Yes, actual software.

I shipped my first commercial software at thirteen. It was shareware[1]Ref. 1shareware en.wikipedia.org door extensions for the Mac Hermes II BBS[2]Ref. 2Hermes II BBS en.wikipedia.org, written in THINK Pascal[3]Ref. 3THINK Pascal en.wikipedia.org.

A door let the BBS hand a caller into an extension for something beyond its built-in functions. People tend to remember games.

The host already had a logged-in user and an active connection, and your extension had to follow the host's conventions. Eventually your extension had to give the caller back, preferably without making the sysop regret ever finding your software.

Displaying the right text was only part of getting it right. If the user entered something unexpected or left, your code still had to respect the state it received and return control cleanly. Otherwise you had built a fancy fucking terminal decoration that trapped the caller.

I wanted the caller to be able to leave!