This mean looking device, built by D-Town Cracka on Flickr, is a Self Propelled Anti-Aircraft Gun, or SPAAG for short. This one is a ZSU-23-4V1 made by the Soviets from 1962, and used in a variety of conflicts since.
Due to its light armour the ZSU-23 was vulnerable to anti-tank and machine guns, and as such was usually placed well behind the front line. However, it was very good at shooting things that weren’t strictly aircraft, and thus it was often deployed to urban environments in places like Syria.
News today from the region indicates further massacres of the Syrian people by their own Government. With Syrians fleeing their homes into Turkey, Iraq and other neighbouring countries the refugee crisis is growing daily. Find out more about the crisis, and what you can do to help, via the UN Refugee Agency.