Recently, the European Metrology Research Programme (EMRP) has funded the IND55 Mclocks joint research project [1] to develop compact and high-performing microwave clocks for industrial applications such as navigation, telecommunication, defence and precision instruments. This project aims at taking full advantage of better performing laser and microwave sources and innovative techniques to prepare and detect the atoms. In this regard, several European national metrological institutes (NMIs) or research institutes, devised new cell-based prototypes that exhibit unprecedented frequency stability performances, of the order of 10-13 at 1 s with a medium long-term in the range of 10-14 or better. Three typologies have been selected: vapour-cell clock based on pulsed optical pumping (POP) [2], on cold atoms [3] and coherent population trapping (CPT) [4, 5, 6]. They are very different and allow matching many industrial applications having different levels of accuracy, stability, compactness, power consumption.