IMPS
India's first round-the-clock instant transfer system, and the rails UPI was later built on.
Immediate Payment Service was launched in November 2010 by NPCI, the same organisation that gave the world UPI six years later. Until then Indian transfers went through NEFT, which settled in periodic batches and only during banking hours. IMPS ran around the clock and moved money in seconds. The payee could be identified by account number and the bank's IFSC code, or by mobile number plus a seven-digit MMID issued by the bank.
MMID never really caught on, since it was yet another number to keep track of. UPI solved the same problem with a readable address and used IMPS as its settlement engine. IMPS lives on for larger transfers, with a ceiling raised to 500,000 rupees in 2021.