@denniew currently openmrs is using the reference application ui though their is work in progress being done to shift to a more modern exciting ui (openmrs microfront ends ) 
You can get started with these resources to learn more about the current openmrs ui
https://wiki.openmrs.org/display/docs/Reference+Application+2.10.0
https://wiki.openmrs.org/display/docs/Using+the+Reference+Application