SigFox is a private company that has built a new IoT technology from scratch, and has made it available as an open standard. It also operates in the industrial, scientific and medical radio frequency band (ISM band), and with the known data traffic restrictions in such band, provides an optimized protocol capable to deliver small data payloads through their ultra-narrow band channelization efficiently, which is unique in the IoT arena.
When the application requirements dictate strict power limitations, and allow for very short data packets and very low data rates, SigFox is a definite option for such applications. The latency provided is rather low, and already limits any real-time or near-real-time applications. SigFox appears to be a well-tailored solution for specific purposes, and its design ethos limits the applicability which makes it a non-competing technology, with respect to cellular systems.