Why Q65 is part of the WSJT-X suite and uses 65-tone frequency-shift keying with long transmit sequences (15 to 300 seconds) and strong forward error correction, which suits the very weak, Doppler-spread, fading signals returned from the Moon. Its submodes let you trade sequence length against speed, so EME operators on VHF, UHF and microwave can decode signals well below the noise floor. It descends from the older JT65 mode that made digital EME popular.
Watch out MSK144 is the tempting one, but its very short 72 ms transmissions are built for meteor scatter pings, not the long path delay and fading of moonbounce; WSPR is a low power propagation beacon mode and PACTOR III is an HF ARQ data mode.
Q65 = Quiet moon (EME); MSK144 = Meteor Streaks; WSPR = whisper beacons.