One system that I’ve made is a population of cylinders that alter in height, in a such way that they lower them selves towards a moveable center (a grande cylinder surrounded by a free space in the form of a circle).
Another system is a population of square building units divided by a variable road. The overall number of building units is set to increase parametrically along with the slider of the road width.
The same system offers another variable; the building units are extruded parametrically by the Z unit vecters as a result of the distance between two moveable points and the base point of each building unit.
Parametric Urbanism Studio 2014 