  The riddle posed by super-Earths (1-4$R_\oplus$, 2-20$M_\oplus$) is that they
are not Jupiters: their core masses are large enough to trigger runaway gas
accretion, yet somehow super-Earths accreted atmospheres that weigh only a few
percent of their total mass. We show that this puzzle is solved if super-Earths
formed late, as the last vestiges of their parent gas disks were about to
clear. This scenario would seem to present fine-tuning problems, but we show
that there are none. Ambient gas densities can span many (up to 9) orders of
magnitude, and super-Earths can still robustly emerge after $\sim$0.1-1 Myr
with percent-by-weight atmospheres. Super-Earth cores are naturally bred in
gas-poor environments where gas dynamical friction has weakened sufficiently to
allow constituent protocores to merge. So little gas is present at the time of
core assembly that cores hardly migrate by disk torques: formation of
super-Earths can be in situ. The picture --- that close-in super-Earths form in
a gas-poor (but not gas-empty) inner disk, fed continuously by gas that bleeds
inward from a more massive outer disk --- recalls the largely evacuated but
still accreting inner cavities of transitional protoplanetary disks. We also
address the inverse problem presented by super-puffs: an uncommon class of
short-period planets seemingly too voluminous for their small masses
(4-10$R_\oplus$, 2-6$M_\oplus$). Super-puffs easily acquire their thick
atmospheres as dust-free, rapidly cooling worlds outside $\sim$1 AU where
nebular gas is colder, less dense, and therefore less opaque. Unlike
super-Earths which can form in situ, super-puffs migrated in to their current
orbits; they are expected to form the outer links of mean-motion resonant
chains, and to exhibit greater water content. We close by confronting
observations and itemizing remaining questions.
