The best alternatives to Reminders API are Later, Hapen, and Retimer. If these 3 options don't work for you, we've listed a few more alternatives below.
Retimer is a handy reminder for repetitive tasks. Just select the requested interval and it will remind you using system notifications. Notifications can be customized and even pinned to the notification drawer so you won't accidentally remove them.
Memo Reminders is application that will help you to do the thing you are often "forgetting", postponing, have a "valid" excuse for not doing it or simply: procrastinating.
Just open Handre, draw a cross, a face, write a text with your finger or anything else. Click “Save” and that's all, reminder is created. Try creating your first reminder with Handre!