This course, "Grokking the System Design Interview", is pretty cool!

A lot of interesting ideas on how to build complex systems.

I'm now going through its sequel ("Grokking the Advanced System Design Interview") which goes into the design of a bunch of distributed systems (e.g. Dynamo, Cassandra, Kafka, ...)

https://www.educative.io/verify-certificate/PMQAVPxzz3ohZ35ZDj9MVoCZpGkA9lOBnhl