What alternatives to SWIFT exist for international payments?

SWIFT is a messaging system used by banks for purposes of payments & settlement. It is not an actual payment system per se.

Anyhow, there are over 1,900+ payment systems in the world. Some are regional to small villages in a very specific geographic area and some are worldwide, like VISA or Mastercard. Less than 3% of all such payment systems are connected. Almost every country has a bunch of local payment systems. QIWI, Boleto, SOFORT, Paypal, WeChat Pay, bKash, JassCash, EasyPaisa, Paytm, etc. are all such examples.