Had to do a force quit, now Hackety just shows an empty screen, with stuff like this to the console:
/Applications/Hackety Hack.app/Contents/MacOS/app/app/db/table.rb:202:in 'match'
or, if I click the left-side buttons, the console says:
"this slot is already being modified by an append, clear, etc"
Should I delete ~/.hacketyhack/+TABLES ?