Short answers, pulled from the story.
Pascal built one of the first mechanical calculators, called the Pascaline, starting in 1642. He also established the carrosses a cinq sols, the first modern public bus service, shortly before his death in 1662. His work on fluid mechanics led to the invention of the hydraulic press and the syringe. He also inadvertently created a primitive form of the roulette wheel while searching for a perpetual motion machine.
Pascal's wager is a probabilistic argument for why one should believe in God. Pascal applied the mathematical concept of expected value, which he had helped develop through his correspondence with Pierre de Fermat, to the question of religious faith. The argument appears in the Pensees under the original title Discourse on the Machine.
The Provincial Letters were an 18-letter series published between 1656 and 1657 under the pseudonym Louis de Montalte. Pascal used them to attack casuistry, an ethical method associated with the Jesuits and particularly with Antonio Escobar. The letters were widely read and influential; Louis XIV ordered them burned in 1660. Writers including Voltaire and Jean-Jacques Rousseau later cited them as a stylistic influence.
In 1654, Pascal corresponded with Pierre de Fermat on gambling problems, specifically on how to divide stakes fairly when a game ends early. From that exchange came the mathematical theory of probability and the concept of expected value. Christiaan Huygens, learning of the work from their correspondence, wrote the first book on the subject. Later figures including Abraham de Moivre and Pierre-Simon Laplace built further on Pascal and Fermat's foundation.
Pascal built on Torricelli's barometer experiments to argue that air pressure decreases with altitude. Too ill to climb the Puy de Dome himself, he had his brother-in-law Florin Perier carry out the experiment on the 19th of September, 1648. Perier confirmed that the mercury column was shorter at the mountain's summit. Pascal replicated the result in Paris by climbing the bell tower of Saint-Jacques-de-la-Boucherie. The SI unit of pressure, the pascal, is named for him.