Toolbox is a tool that offers a familiar RPM based environment for developing and debugging software that runs fully unprivileged using Podman.
The toolbox container is a fully mutable container; when you see "yum install ansible" for example, that's something you can do inside your toolbox container, without affecting the base operating system.
This is particularly useful on OSTree based Fedora systems like Silverblue. The intention of these systems is to discourage installation of software on the host, and instead install software as (or in) containers.
However, this tool doesn't require using an OSTree based system — it works equally well if you're running e.g. existing Fedora Workstation or Server, and that's a useful way to incrementally adopt containerization.