Faker (JavaScript)
Fake but realistic data for testing, in the browser and Node.js
Datafaker
Fake data generator for the JVM
Bogus
Fake data generator for C#, F# and VB.NET
Instancio
Automatically populated objects for Java unit tests
Synthetic Data Vault (SDV)
Synthetic tabular data generation with generative models
Mockaroo
Online generator of realistic test data and mock APIs