rkt is described as 'is the next-generation container manager for Linux clusters. Designed for security, simplicity, and composability within modern cluster architectures, rkt discovers, verifies, fetches, and executes application containers with pluggable isolation' and is an app in the Network & Admin category. There are more than 10 alternatives to rkt for a variety of platforms, including Linux, Mac, Windows, Self-Hosted solutions and Minecraft. The best alternative is Docker, which is both free and Open Source. Other great apps like rkt are Flatpak (Free, Open Source), Podman (Free, Open Source), AppImageKit (Free, Open Source) and Singularity (Free, Open Source).
podman is a daemonless container runtime for managing containers, pods, and container images. It is intended as a counterpart to CRI-O, to provide low-level debugging not available through the CRI interface used by Kubernetes.
The FreeBSD jail mechanism is an implementation of operating system-level virtualization that allows system administrators to partition a FreeBSD-based computer system into several independent mini-systems called jails.