Vitrification is one of the safest technologies for the stabilization of inorganic waste. Being capital and energy intensive, its application to industrial waste (such as mining residues, ashes, slags, i.e. beyond radioactive waste) is controversial. A key to sustainability is represented by the definition of useful products, from the reuse of waste-derived glasses, to generate extra revenues. Typical products consist of dense and porous glass-ceramics, from viscous flow sintering of fine glass powders with concurrent crystallization. Dense glass-ceramics, developed from waste-derived feedstock and fired at temperature not exceeding 1000 °C, may offer superior strength and hardness, compared to stoneware ceramics, developed from natural raw materials and fired above 1100 °C. Porous glass-ceramics combine, compared to polymer-based thermal insulators, superior strength and durability: a long service life obviously maximizes the energy saving. In the perspective of valorisation of waste-derived glasses, new opportunities rely on alkali activation, i.e. on the suspension of waste-derived glass powders in aqueous solution of alkali hydroxides, resulting first in surface dissolution and then in progressive hardening, due to condensation reactions occurring to dissolution products (at 40-75 °C). Before complete gelation, suspension may be conveniently foamed, just by intensive mechanical stirring (also with the help of surfactants). Highly porous glass-ceramics are achieved by sinter-crystallization of foamed suspensions, with a clear advantage on conventional methodology, involving gas release by additives operating during sintering: beyond avoiding extra costs from additives (such as SiC), the new method prevents risks of inhomogeneity, resulting from the contrast between gas expansion (requiring low viscosity) and crystallization (increasing the viscosity of softened glass). Alkali activation is not just a processing tool: according to the engineering of the chemical composition (namely Na2O/SiO2, CaO/SiO2, Al2O3/SiO2 ratios) of waste-derived glass, dissolution and condensation reactions may be tuned in order to provide highly durable (Ca- and Na-) alumino-silicate hydrated gels, defining new construction materials (possibly replacing conventional cements) without any thermal treatment.