Postal : Postal is a complete and fully featured mail server for use by websites & web servers. Think Sendgrid, Mailgun or Postmark but open source and ready f...
Matrix : Matrix is an open standard for decentralised communication, providing simple HTTP APIs and open source reference implementations for securely distribu...
Mockoon : Mockoon is the easiest and quickest way to design and run mock APIs. No remote deployment, no account required, free and open-source.
npoint.io : JSON storage bins with schema validation
Cool QL Cool : CoolQLCool (CQC) is an open source GraphQL server that allows you to turn websites into GraphQL APIs.
Free and Open Source tool for building mock APIs. Create stable development environments, isolate yourself from flakey 3rd parties and simulate APIs that don't exist yet.