GraphiQL is described as 'Browser-based IDE for exploring GraphQL' and is an app in the Development category. There are three alternatives to GraphiQL for Online / Web-based and Self-Hosted solutions. The best alternative is GraphQLZero, which is both free and Open Source. Other great apps like GraphiQL are GraphQl Editor (Freemium, Open Source) and GraphQL Playground (Free, Open Source).
GraphQLZero is a free, online GraphQL API that you can use to get fake data from a real backend while testing or prototyping your app. It is inspired and powered by JSONPlaceholder, serving the same dataset but in the form of a GraphQL server.
GraphQL Playground is an IDE for better development workflows (GraphQL Subscriptions, interactive docs & collaboration). You can download the Electron-based desktop app or use the web version at graphqlbin.com.