How Extreme Can Planetary Systems Be?

The first system of extrasolar planets was found in orbit about a pulsar. The next was a giant planet, in a 4 day orbit, and following that a more massive giant ill all eccentric orbit. These types of planetary systems were. not expected prior to being found. What else is out, there, in our galaxy? Dynamical stability (for a large number of orbits) is a requirement, but beyond that what restrictions are there? For instance, a nearly coplanar system analogous to our solar system but, with planets alternating between prograde and retrograde orbits with increasing distance from star could survive for a long time, but, no plausible model of its formation (apart from construction by a technologically advanced Civilization) exists. A pure lead planet could survive, but how could such a planet, form? These and other speculations are discussed, together with a sobering assessment of our ability to make predictions of exoplanet characteristics.