#queues
2 tools

Zeplo
★ 2.0Zeplo lets developers add retry, delay, queue and schedule to HTTP endpoints without setting up Redis, RabbitMQ or SQS. Just prefix any HTTP endpoint with zeplo.to/ and the request is queued.
PaidMacWindows

slashQ
★ 2.5slashQ is an appointment scheduling and queue management tool that helps businesses manage customer flow. With slashQ organizations and businesses can eliminate lines and improve customer satisfaction while avoiding congestion and ensuring social distancing.
PaidSoftware as a Service SaaS