Recently developed fundamental mode orthogonal fluxgate (FM-OFG) offers high sensitivity sensing systems for magnetic signals with the amplitude ranging 1pT∼10µT. The mechanism of the FM-OFG is reviewed briefly and various sensors made based on it are presented. Magnetic field from human heart is measured with an array of 36 channels of FM-OFG magnetometers. Also shown are several applications using gradiometers built by extending a magnetometer design, including detection of lightening residue and of magnetic nanoparticle sample.