Mininet can leverage the applications installed in the server to attach them as processes to the hosts that it emulates. For example, see the following, a vim started from a host in Mininet:

$ sudo mn
*** Creating network
*** Adding controller
*** Adding hosts and stations:
h1 h2 
*** Adding switches and access point(s):
s1 
*** Adding link(s):
(h1, s1) (h2, s1) 
*** Configuring hosts
*** Starting controller(s)
c0 
*** Starting switches and/or access points
s1 ...
*** Starting CLI:
mininet-wifi> h1 vim
  

The preceding command will open a vim instance in the Terminal! You may even try other applications such as gedit, or even mininet itself, to run as a process attached to the emulated host. However, note that these are real processes from the applications that are installed on the server. Not an emulation.

Containernet extends Mininet to use Docker containers as hosts in Mininet emulations, by extending the host class of Mininet. Hence, container enables emulation of more interesting and complex functionalities, attaching Docker containers directly as hosts. This allows the programs installed in a container available to the host.