  Upcoming cosmological surveys have the potential to reach groundbreaking
discoveries on multiple fronts, including the neutrino mass, dark energy, and
inflation. Most of the key science goals require the joint analysis of datasets
from multiple surveys to break parameter degeneracies and calibrate
systematics. To realize such analyses, a large set of mock simulations that
realistically model correlated observables is required. In this paper we
present the N-body component of the HalfDome cosmological simulations, designed
for the joint analysis of Stage-IV cosmological surveys, such as Rubin LSST,
Euclid, SPHEREx, Roman, DESI, PFS, Simons Observatory, CMB-S4, and LiteBIRD.
Our 300TB initial data release includes full-sky lightcones and halo catalogs
between $z$=0--4 for 11 fixed cosmology realizations, as well as an additional
run with local primordial non-Gaussianity ($f_{\rm NL}$=20). The simulations
evolve $6144^3$ particles in a 3.75$\,h^{-1} {\rm Gpc}$ box, reaching a minimum
halo mass of $\sim 6 \times 10^{12}\,h^{-1} M_\odot$ and maximum scale of $k
\sim 1\,h{\rm Mpc}^{-1}$. Instructions to access the data, and plans for future
data releases, can be found at https://halfdomesims.github.io.
