I don't know much about Hazelcast, but it seems to just be a group of distributed versions of constructs used for managing threads. That's the key difference. Akka abstracts thread management for you with an Actor model, which imo is much much easier to use.
It's a concurrency framework that allows you to:
1) abstract threads into actors and messages
2) distribute processing with remote actors residing on different machines.
imo, it's way easier to use than traditional java concurrency