The Signal messenger and protocol.

Signal’s operating costs: around $40 million this year

• $14 million a year in infrastructure costs
• $6 million annually, goes to telecom firms to pay for the SMS text messages Signal uses to send registration codes to verify new Signal accounts’ phone numbers
• $19 million a year or so out of Signal’s budget pays for its staff. Signal now employs about 50 people

Staff budget seem crazy high with about 50 people. That's an average of $31.666 per month per employee.