  We present designs for scalable quantum computers composed of qubits encoded
in aggregates of four or more Majorana zero modes, realized at the ends of
topological superconducting wire segments that are assembled into
superconducting islands with significant charging energy. Quantum information
can be manipulated according to a measurement-only protocol, which is
facilitated by tunable couplings between Majorana zero modes and nearby
semiconductor quantum dots. Our proposed architecture designs have the
following principal virtues: (1) the magnetic field can be aligned in the
direction of all of the topological superconducting wires since they are all
parallel; (2) topological $T$-junctions are not used, obviating possible
difficulties in their fabrication and utilization; (3) quasiparticle poisoning
is abated by the charging energy; (4) Clifford operations are executed by a
relatively standard measurement: detection of corrections to quantum dot
energy, charge, or differential capacitance induced by quantum fluctuations;
(5) it is compatible with strategies for producing good approximate magic
states.
