Red matter was a substance that was created through the use of Decalithium. It was created by the Vulcan Science Academy and took the form of a red liquid substance that collected in the form of a sphere. A single drop of this compound was capable of creating a singularity. Red matter must first be ignited for the condensation into a singularity to occur. Red matter is highly unstable and can easily be ignited by conventional methods such as heat or shock much like gun powder.
By 2387, the Vulcan government had developed the ability to produce red matter. At the time, the Hobus star had grown increasingly unstable and was going to produce a powerful shockwave that would have destroyed the Romulan homeworld of Romulus. The only way to stop the destruction of the star was by using red matter to collapse it into a singularity. The Romulan Star Empire briefly considered invading the planet Vulcan in order to acquire the technology which the Vulcans refused to share. Ambassador Spock was able to get enough red matter manufactured which was deployed on the Starfleet ship Jellyfish. However, Spock was too late as the supernova from Hobus destroyed Romulus and extinguished the lives of millions of Romulan's. Before the nova could progress further, Spock shot a portion of the red matter into the Hobus star collapsing it into a singularity.
Due to the effectiveness of the Red matter in the destruction of the Hobus supernova, the Federation began weaponizing it. A "rift generator" was made, which uses a very small amount to create spatial rifts strong enough to drag passing ships out of warp and keep them in normal space within a certain radius. Though it has not been proven, the use of Red matter to make black-hole-generating torpedo-bombs have been rumored.