Is Talk Calendar available to non-users of KakaoTalk?
If you have a Kakao account, you can use the Talk Calendar on the web even if you have never signed up for KakaoTalk or do not have the KakaoTalk app.
Talk Calendar Web:

Later on, if you sign up for or log in KakaoTalk with the same Kakao account, you can view the same schedule information in the Talk Calendar within the KakaoTalk app.