  In the present report, a set of theoretical results obtained in the period
from 1991 to 2005 are reviewed. The physical systems under study include quark
models of hadrons, inert atom clusters, atomic traps, and electrons and
excitons confined in quantum dots. They contain three or more particles, and
are described by nonrelativistic Quantum Mechanics. In the smallest systems (6
particles or less), exact diagonalization complemented with the Lanczos
algorithm, and some analytical approaches (1/D-expansion, improved
semiclassical quantization, etc.) are used. In the larger systems (from 7 to
hundreds of particles), we employ approximate methods, such as two-point Pade
approximants, variational Monte Carlo estimations, Hartree - Fock and RPA
schemes, BCS functions and the Bethe - Goldstone algorithm, etc. With the help
of these methods, a variety of physical properties have been computed, i.e.,
energy spectra, particle densities, spin textures, light absorption and
emission, inelastic light scattering, and some dynamical features.
