I have some experience with Seastar.

Seastar and Silk are both event-driven, thread-per-core platforms with synchronization and scheduling facilities built-in.

Seastar is meant to be an integrated platform so it includes I/O and networking primitives for high-performance storage and socket operations to boot.

Silk does not appear to take an opinion on how the actual work performed on the thread should be architected

I just took a look a both (thanks for the pointer to seastar! cool project). I'd say "sort of but not exactly". It seems like two approaches to solving the same problem.

Silk seems like mostly a scheduler that uses C++'s native coroutines. Seastar is a future-based framework. Both contain a scheduler and enable async coding patterns.