Penpot: The open-source design tool for design and code collaboration

Collection of custom elements that appear hand drawn. Great for wireframes or a fun look.

The Pencil Project's unique mission is to build a free and opensource tool for making diagrams and GUI prototyping that everyone can use.

Design and prototype customized UI, interaction, navigation, transition and animation for App Store ready Apps in Interface Builder with IBAnimatable.

Mockoon is the easiest and quickest way to run mock APIs locally. No remote deployment, no account required, open source.

🎨 React application prototyping tool for developers and designers 🏗️

dnd visual editor - mockups and code in one go!

Turn Python scripts into handouts with Markdown and figures

DEPRECATED: Multiplatform GUI Prototyping/Wireframing

Quickly try out any Swift pod or framework in a playground

A Ruby DSL for prototyping card games.

Business database for non-programmers. Universal UI, simple-code logic, automatic actions, access rules, logging, API and more. Quickly create a complex internal apps using the database as an interface.

✔️ Mock data for your prototypes and demos. Remote deployments to Zeit now.

Browser-based MDX editor

Mmock is an HTTP mocking application for testing and fast prototyping

🚧 Build web pages with Vuse, the next-gen interactive page builder powered with Vue.js.

Charm: A Framework for Rapidly Prototyping Cryptosystems

IBM TJBot

PHONK is a coding playground for new and old Android devices

Fake JSON Server is a Fake REST API that can be used as a Back End for prototyping or as a template for a CRUD Back End.