  We show initial results from our ongoing HST GHOSTS survey of the resolved
stellar envelopes of 14 nearby, massive disk galaxies. In hierarchical galaxy
formation the stellar halos and thick disks of galaxies are formed by accretion
of minor satellites and therefore contain valuable information about the
(early) assembly process of galaxies. We detect for the first time the very
small halo of NGC4244, a low mass edge-on galaxy. We find that massive galaxies
have very extended halos, with equivalent surface brightnesses of 28-29
V-mag/arcsec^2 at 20-30 kpc from the disk. The old RGB stars of the thick disk
in the NGC891 and NGC4244 edge-on galaxies truncate at the same radius as the
young thin disk stars, providing insights into the formation of both disk
truncations and thick disks. We furthermore present the stellar populations of
a very low surface brightness stream around M83, the first such a stream
resolved into stars beyond those of the Milky Way and M31.
