So long, and thanks for all the fish...
After 13 years in business, Circus Ponies Software has shut down. It was a good run.
If you need a copy of NoteBook 4.0 (3.x and earlier don’t run on OS X El Capitan) or need technical support, you can try sending an e-mail to support@circusponies.com. There's a chance someone will respond but no guarantees.