Resque was the main inspiration, Sidekiq still provides compatibility with some of its APIs to this day.

https://github.com/sidekiq/sidekiq/blob/ba8b8fc8d81ac8f57a55...

Sidekiq credits BackgrounDRb and Delayed::Job and Resque as inspiration here: https://www.mikeperham.com/2022/01/17/happy-10th-birthday-si...

The API is very close, but architecturally it's different.

Additionally, delayed_job came before resque.