empty - empty is an utility that provides an interface to execute and/or interact with processes under...

Podman - Simple debugging tool for pods and images

Expect - Expect is a tool for automating interactive applications such as telnet, ftp, passwd, fsck, rlogin...

containerd - An industry-standard container runtime with an emphasis on simplicity, robustness and portability

Check - Check is a unit testing framework for C, which runs on environments such as GNU/Linux, GNU/Hurd, BSD, and Mac OSX. 

LXD - Daemon based on liblxc offering a REST API to manage containers