Project Shiva was a Romulan Star Empire weapon experiment designed to create more powerful weaponry that was capable of destroying a ship in a single strike.
A prototype version of the Project's research was present on the starship IRW Melak which was assigned to destroy a test object within the Romulan Neutral Zone. Something that both the Federation and Klingon Empire protested; both of whom sent starships to intercept the test ship. The USS Explorer was on its way but was beaten to the Melek by a Klingon D-7 Battle Cruiser which demanded the experiment to end. The Romulan crew ignored the Klingon protests and fired the weapon which created a powerful shockwave that send the Klingon ship spinning of course. The Melek itself struggled to maintain its shields as the explosion ripped a hole through subspace.
After the shock wave was over and radiation levels returned to normal, the crew of the Melek believed that the experiment was a success. That was until an intense gravity well was detected which destroyed the Melek. It is possible that the project was deemed a failure.
As a result of Project Shiva, the region of space filled with inhabitable planets known as Tabula Rasa was created which all three empires attempted to colonise. After encountering the danger posed by the Metar, a second, more powerful Shiva Device (also known as the Anomaly Device) was detonated which was responsible for sealing the subspace anomaly. (TOS video game: New Worlds)