I will briefly introduce several activities of the Group of High-Energy Astrophysics of the AI in Ondrejov (mostly in collaboration with other Institutes): (1) Development of X-ray optics for future astronomical missions including Lobster-Eye optics (2) Robotic Telescopes and related investigations of Gamma Ray Bursts (GRB) and Optical Transients (OTs) (3) Alternative detections of GRBs and OTs - ionospheric SID monitors and all sky cameras (4) Low dispersion spectroscopy with ESA Gaia and (5) Optical analyses of HE objects using astronomical archival plates.