  We review topics in searches for axion-like-particles (ALPs), covering
material that is complementary to other recent reviews. The first half of our
review covers ALPs in the extreme environments of neutron star cores, the
magnetospheres of highly magnetized neutron stars (magnetars), and in neutron
star mergers. The focus is on possible signals of ALPs in the photon spectrum
of neutron stars and gravitational wave/electromagnetic signals from neutron
star mergers. We then review recent developments in laboratory-produced ALP
searches, focusing mainly on accelerator-based facilities including beam-dump
type experiments and collider experiments. We provide a general-purpose
discussion of the ALP search pipeline from production to detection, in steps,
and our discussion is straightforwardly applicable to most beam-dump type and
reactor experiments. We end with a selective look at the rapidly developing
field of ultralight dark matter, specifically the formation of Bose-Einstein
Condensates (BECs). We review the properties of BECs of ultralight dark matter
and bridge these properties with developments in numerical simulations, and
ultimately with their impact on experimental searches.
