Project Greengrid was a project developed by Stark Industries. It was the company's first steps in developing the atmosphere's capacity for storing and transmitting power, essentially weaponizing the sky itself. It was later hijacked by Kearson DeWitt and Ultimo.
By starting a power transmission through ionization, Stark Industries were able to create highly charged storm activity. Their intention was to use it to store and transmit power. Since they were developing it for the United States Armed Forces as part of a weapons contract, they were essentially weaponizing the sky itself.
Having successfully stolen the Dataspine (an archived version of J.A.R.V.I.S.) and modified it with Project P.R.O.T.E.A.N., Kearson DeWitt of A.I.M. was able to create Ultimo. Merging himself physically and mentally with this giant A.I. through use of P.R.O.T.E.A.N., DeWitt was able to access all of the information archived by J.A.R.V.I.S., including Project Greengrid.
At an A.I.M. base in Malaysia, DeWitt/Ultimo put the project into effect, creating a typhoon. When Iron Man and War Machine attacked the base with a reprogrammed Arc Armiger, A.I.M. put up a fight with their soldiers and technology. Rhodes located the Greengrid power nexus beneath the epicenter of the storm. By repositioning the Greengrid relays and destroying the central power structure, he was able to send the generator into meltdown, terminating the project.
During the final battle against Ultimo at the Stark Archives, S.H.I.E.L.D. attempted to destroy it by using reprogrammed technology from Project Greengrid, but Ultimo took control of it and attempted to use it against them.