Onoff is a SaaS product offered by Onoff Telecom, a telecommunications operator. The product aims to solve business problems related to telecommunications by offering virtual numbers that can be used for various purposes. One of the key features of Onoff is the ability to get a French number, which includes national calls, unlimited SMS in France, and no contract. The product also offers a range of features, although specific details are not provided in the given text. Users are encouraged to visit the Features page on the website to discover the cool features that Onoff proposes.