23: Receive digimodes from other countries
I found some other strange signals on the 30-meter band. The Signal Identification Wiki was really helpful for figuring out what they were: https://www.sigidwiki.com/wiki/FT8
FT8 is a new protocol, invented in 2017, and it seems to be super popular right now! It allows you to transmit short messages, and again, people are looking for people to talk to (CQ), saying how well they receive each other, or saying goodbye (73).
This is the WSJT-X software.