The best alternatives to knoc.me are Mapped, Snapslack, and unSend.it. If these 3 options don't work for you, we've listed a few more alternatives below.
Are you a startup founder? Great! Mapped is a mobile app for you to learn from more advanced founders fast. You can ask questions and instantly see founders who already answered similar ones, with the answers included. It is available for free!
PhoneTag is a new fun messaging service and social game that enables you to instantly send disappearing voice messages with funny voice filters including autotune to friends and family.