I'm a fairly rational person, and I'm not particularly religious. I'm mostly interested in Judaism because of cultural heritage. I know I ran across somewhere something about 'semitic cultures' and 'semitic languages', but I'm not super familiar with them. I mostly grew up thinking that the Jews were the only Semites in the world, but a recent reflection tells me that this was likely not the case. Were other cultures, such as the Canaanites and the Babylonians also considered Semites? Or were they something different?
Semitic is a term that refers to both a very large language family and a somewhat outdated term for racial/ethnic classification. The term comes from Shem, one of the sons of Noah.
As a language family, Semitic itself is part of the larger Afro-Asiatic group, which encompasses North Africa and the Middle East. Besides Hebrew, other living Semitic languages include Arabic and Amharic (the official language of Ethiopia).
To answer the second part of your question, Canaanites and Babylonians were indeed Semitic speaking peoples, with Babylonians speaking Akkadian and the Canaanite languages evolving into Hebrew and Phoenician. The Phoenicians went on to create the Phoenician alphabet, which is the basis for most writing systems in the world, including Arabic, Hebrew and the Latin Alphet, to name a few. The Phoenicians also founded Carthage. You'll find that many groups of ancient people who had their origins in the Levantine coast were Semitic speakers.
So no, the Jews are not alone in being Semites, certainly not by the linguistic definition of the word. Antisemitism, however, is a word that has evolved to refer to Jewish people solely.