Redis is a database management system (DBMS). Badger is a storage engine.
An application developer would not choose Badger, but instead would pick a DBMS such as Redis.
A database engineer would use Badger to develop a DBMS that the application engineer could use. If the database engineer so chooses they could expose a Redis compatible API.
An application developer would not choose Badger, but instead would pick a DBMS such as Redis.
A database engineer would use Badger to develop a DBMS that the application engineer could use. If the database engineer so chooses they could expose a Redis compatible API.