Nitrogen fixation is taking nitrogen from the air and turning it into organic compounds in the soil. It is the backbone of building soil. Certain plants are especially good at nitrogen fixation, which makes them useful for improving soil.
Examples for nitrogen fixers: legumes (beans, soybeans, peas, lupines). Also Azolla which exists in symbiosis with nitrogen-fixing microalgae.
This nitrogen fixer would be incredible as an open source machine.