A major challenge in nanotechnology is the fabrication of complex three-dimensional (3D) structures with desired materials. We present a strategy for fabricating arbitrary 3D nanostructures with a library of materials including metals, metal alloys, 2D materials, oxides, diamond, upconversion materials, semiconductors, polymers, biomaterials, molecular crystals, and inks. Specifically, hydrogels patterned by femtosecond light sheets are used as templates that allow for direct assembly of materials to form designed nanostructures. By fine-tuning the exposure strategy and features of the patterned gel, 2D and 3D structures of 20- to 200-nm resolution are realized. We fabricated nanodevices, including encrypted optical storage and microelectrodes, to demonstrate their designed functionality and precision. These results show that our method provides a systematic solution for nanofabrication across different classes of materials and opens up further possibilities for the design of sophisticated nanodevices.