Update containers.md

tools-and-tech/containers.md

+OS namespaces, aka containers, purport greater security than process isolation
+without needing to impose the performance cost of a virtual machine. 
 
+# 
+
+## Application containers
+
+Intended to host a single application.
+
+- [singularity][]
+- [podman][]
 - docker
+- [cri-o](https://github.com/kubernetes-sigs/cri-o)
+- [containerd](https://github.com/containerd/containerd)
+- [gvisor](https://gvisor.dev/)
+
+
+## System containers
+
+Lightweight VMs
+
 - [lxd][]
+
+## "Lightweight VMs"
+
+- Kata containers
+
+## Other
+
+Need to do more research here.
+
 - rkt
-- [singularity][]
+
+# OCI runtimes
+
+- [crun](https://github.com/containers/crun)
+- [runc](https://github.com/opencontainers/runc)
+
+
+# Windows containers
+
+- https://github.com/Microsoft/hcsshim
+
+# More stuff
+
+- https://github.com/moby/moby
 
 [lxd]: https://linuxcontainers.org/
+[podman]: https://podman.io/
 [singularity]: https://github.com/sylabs/singularity