non-aqueous solvents
Water is the default solvent in our minds, but it is a tyrant: it levels strong acids and strong bases, it reacts with very reactive substances, and its own acid-base window (from H3O+ down to OH-) is fairly narrow. To do chemistry that water forbids — to isolate a super-strong acid, to dissolve a free electron, to react a substance that would simply hydrolyze in water — chemists deliberately work in non-aqueous solvents: liquid ammonia, anhydrous sulfuric acid, liquid hydrogen fluoride, glacial acetic acid, BF3 systems, molten salts, and the familiar organic solvents.
Each non-aqueous solvent opens a different acid-base window and a different stage for reactivity. Liquid ammonia (boiling at minus 33 degrees C) is more basic than water and a far better proton acceptor, so it levels acids harder but lets you compare and use very strong bases; famously, alkali metals dissolve in it to give brilliant blue solutions of solvated free electrons, which are powerful reducing agents impossible in water. Anhydrous sulfuric acid is the opposite extreme: it is so acidic and so unwilling to accept protons that even nitric acid behaves as a base in it (HNO3 + 2 H2SO4 gives NO2+ + H3O+ + 2 HSO4-, the very nitronium ion that nitrates benzene). Liquid HF is wonderful for fluoride chemistry and for generating powerful fluorinating and oxidizing conditions. Molten salts dissolve metal oxides and let high-temperature electrochemistry happen.
Choosing the solvent is itself a chemical decision. It sets which acids and bases can coexist, which species are stabilized, and what reactions become possible. This is exactly the territory of the leveling effect and the solvent-system concept: many non-aqueous solvents self-ionize just as water does (2 H2O gives H3O+ + OH-), and you can define acids and bases relative to that solvent's own cation and anion. Non-aqueous chemistry is where superacids, superbases, noble-gas fluorides, and many reactive inorganic species were first tamed.
Dissolve sodium metal in liquid ammonia and you get a deep blue solution: Na gives Na+ plus an electron solvated by ammonia molecules. That free 'electride' electron is a powerful, clean reducing agent (used in Birch reductions) and simply cannot exist in water, which it would reduce to H2.
Liquid ammonia stabilizes solvated electrons — chemistry water simply forbids.
Switching solvents does not change a substance's intrinsic nature, only what you can observe and stabilize. The same proton transfer that water levels becomes measurable in a less basic solvent — the chemistry was always there; water was just hiding it.