  The Observatory Science Operations (OSO) subsystem of the SKAO consists of a
range of complex tools which will be used to propose, design, schedule and
execute observations. Bridging the gap between the science and telescope
domains is the key responsibility of OSO, requiring considerations of
usability, performance, availability and accessibility, amongst others. This
paper describes the state of the observatory software as we approach
construction milestones, how the applications meet these requirements using a
modern technology architecture, and challenges so far.
