I am setting up an Openstack cloud based on MAAS and Juju. Once I have this cloud ready then is it possible to Run different operating systems on this cloud or its limited to Ubuntu OS only. Remember I am not talking about Base OS used by MAAS but the operating system that I am gonna use later in 'i think' Openstack dash board or somewhere on top of this cloud. I have got some tiny OS that I want to RUN on this cloud so is that possible or Ubuntu Cloud Infrastructure does not support any other operating system then Ubuntu.
MAAS and Juju are designed to deploy the Ubuntu operating system primarily. You will able to successfully use MAAS and Juju to run your Openstack cloud. As Huygens mentioned, you will be able to create VMs that running many different operating systems.
However, Juju is designed to deploy VMs that run an Ubuntu operating systems. This means that if you want to use the juju command to deploy VMs and VM clusters, they will have to be using the Ubuntu operating system.
Fracisco Souza of Globo.com, Brazil's largest TV network, has posted info on how Globo has modified Juju to be able to deploy CentOS. Besides that, Juju can't currently deploy any other OS.
You can run any OS that is supported by KVM and by your CPU. Examples are for a typical x86_64 CPU: most of the BSD family, most Linux based Distro, Windows, etc.
Note that some OS have requirements, so you need to be able to cover those when setting up a VM to be able to run the OS.