Nanoelectronic devices can provide versatile and relatively simple systems to study complex quantum phenomena under well-controlled, adjustable conditions. Existing technologies enable the fabrication of low-dimensional nanostructures, such as quantum dots (QDs), in which it is possible to add or remove individual electrons, turn on and off interactions, and tune the properties of the confined electronic states, simply by acting on a gate voltage or by applying a magnetic field. The hybrid combination of such nanostructures, having microscopic (atomic-like) quantum properties, with metallic elements, embedding different types of macroscopic electronic properties (due, e.g., to ferromagnetism or superconductivity), can open the door to unprecedented research opportunities. Hybrid nanostructures can serve to explore new device concepts with so far unexploited functionalities and, simultaneously, provide powerful tools to study fundamental aspects of general relevance to condensed-matter physics. Only recently, following progress in nanotechnology, have hybrid nanostructures become accessible to experiments.Here we propose an original approach that takes advantage of recently developed self-assembled QDs grown on Si-based substrates. These QDs have many attractive properties (well-established growth, ease of contacting, etc.). We will integrate single and multiple QDs with normal-metal, superconducting, and ferromagnetic electrodes and explore device concepts such as spin valves, spin pumps, and spin transistors (a long standing challenge). Using these hybrid devices we will study spin-related phenomena such as the dynamics of confined and propagating spin states in different solid-state environments (including superconducting boxes), long-distance spin correlations and entanglement. The new knowledge expected from these experiments is likely to have a broad impact extending from quantum spintronics to other areas of nanoelectronics (e.g. superconducting electronics).