Dimensional Developments was a research company.
It was part of the maze surrounding Veidt Enterprises. It funded the Institute for Extraspatial Studies. In turn, it was funded by Pyramid Deliveries. Veidt financed DD with the proceeds of the spark hydrants he developed.
Dr. Mahattan's past associates, Janey Slater, Wally Weaver were employees of the firm. All of them were unwittingly exposed to radiation and later suffered cancer. They were used as part of a plan by Veidt to get rid of Dr. Manhattan.
Following this plan, when Moloch got out from prison, Adrian Veidt offered him a temporary job, presenting him a chance to atone himself from his past life. He worked in an enclosed office comparing and cross-checking the results from research teams testing a new energy source. He didn't know that Veidt introduced some errors himself to check if Moloch could detect them. Veidt had hid a radioactive source in his office in order to cause cancer to him.
Dimensional Developments apparently did all the research concerning teleportation, ultimately triggering the Alien Monster.