Collecting fares. A metro or bus system needs gates and readers, and a back office. The back office works out each fare, keeps the accounts, and shares the money among operators when one trip uses more than one. The industry calls the whole system automatic fare collection. Riders pay in two main ways:

Automatic fare collection: riders pay with a closed-loop card or with any bank card or phone at the gate, and the back office works out each fare, keeps the accounts and shares the money among operators.

India's National Common Mobility Card aims to let one card pay for metros, buses and shops across the country.

Collecting tolls. Electronic tolling reads a tag, or the number plate, and charges the owner's account. The next step is free-flow tolling, with no booths at all. Readers on a frame above the road, called a gantry, charge each vehicle as it passes at full speed. Behind the road sits a large back office. It matches each passage to an account, sends bills, and chases unpaid tolls. In India, many toll roads are built and run by private companies, which collect the tolls under long contracts with the government.

Free-flow tolling: readers on a gantry above the road read each vehicle's tag or number plate at full speed, and the back office matches the passage to an account, sends the bill and chases unpaid tolls.

Parking and the kerb. Cities also manage the space beside the road, the kerb, for parking, loading and picking up passengers. Software sets the charges and takes payment by app.

Who buys. The buyers are city transport authorities, metro and bus companies, toll-road operators and city governments. They buy through tenders. The systems they buy run for decades, and are now moving from cash and tickets to phones and bank cards.

Every company named here has posted software engineering jobs in India. Famous companies that don't actively hire software engineers in India are left out.