The Folks at Carnegie Melon
have been messing around with modular servo rings that they string together into a snake that can do a lot when it comes to mobility.
drones with this form type would be ideally useful for infiltration via pipes, cable runs, ductwork, and crawlspaces. not to mention being commercially available for inspection of same.
for those like spiders, This guy has some pretty amazing stuff. bonus: he programs the movement in the video using excel spreadsheets.