These small utilities allow creating very lightweight job queue
systems which require no setup, maintenance, supervision, or any
long-running processes.

The intended purpose is ad-hoc queuing of command lines (e.g. for
building several targets of a Makefile, downloading multiple files one
at a time, running benchmarks in several configurations, or simply as
a glorified nohup), but as any good Unix tool, it can be abused for
whatever you like.