I read somewhere that grape tomatoes are the newest development in tomatoes! When I was growing up, we called these plum tomatoes, not like the canning plum tomatoes, but miniature plum tomatoes. Because they are produced in abundance, they were used to make sauce just like their larger cousins. Not particularly sweet but rich in tomato flavor.
There was a red plum and a yellow plum available in seed catalogs from the 1800's and then Charlie Rick ( a renown tomato breeder at the University of California -Davis until his death a few years ago) sent me a Pink Plum, which he said was one of his favorite tomatoes. Dr. Rick was a plant explorer, and the authority on tomato genetics. He traveled throughout South America, Central America, Mexico, the Galapagos and the Caribbean looking for new tomato species and variants. Through his work, and the wild tomato genes he introduced into traditional canning tomato varieties, the California processed tomato industry was born and thrived. One day David Cavannaugh from the Seed Savers Exchange showed him a tomato they grew at Heritage Farm from some seed we were selling at the time , a bizarre green fruited variety that split open like a fuzzy capsule when it ripened (which I obtained in a batch of seed from New Zealand several years earlier). He sent me a nice note and we began to correspond with one another.
Pink Plum was a little rose beauty from Cuba that he said he used to make a nice sweet tomato sauce.
I noticed that, much like current tomatoes, these little plum tomatoes produced more variation after being grown alongside of cherry tomatoes and current tomatoes. They cross easily. Sweetie, Sweet 100 and Gardeners Delight were very similar cherry tomatoes that were available through by seed retailers in the 1980's. They were sensational because they were sweet, really sweet. They were the perfect snacking tomato. A tomato kids could love. Suddenly, the plums became sweeter. It's not too difficult to imagine how the popular hybrids like Santa and Juliette were developed.
There were also pear tomatoes (no, not the pear shaped canning tomatoes), little inch or so long mini pears with a distinct neck like a bosc pear. These too have been known since the 1800's. Distinctive, ornamental and fun to grow, this group consisting of many distinct lines of yellow, red and pink fruit and are often ignored by gardeners and hybridizers.
Very small pear shaped fruit in red and yellow, interesting currant x salad pear tomato cross from Mexico, pronounced neck and much smaller than other common little pear tomatoes. Great in salads, hearty flavor, crisp and crunchy.