The best open source alternative to OpenFL is LÖVE, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to OpenFL and 12 is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to OpenFL are Pygame (Free, Open Source), MonoGame (Free, Open Source), nCine (Free, Open Source) and FreeBASIC (Free, Open Source).
Pygame is a set of Python modules designed for writing video games. Pygame adds functionality on top of the excellent SDL library. This allows you to create fully featured games and multimedia programs in the python language.
One framework for creating powerful cross-platform games. The spiritual successor to XNA with 1000's of titles shipped across desktop, mobile, and console platforms. MonoGame is a fully managed .NET open source game framework without any black boxes.
FreeBASIC is a completely free, open-source, 32-bit BASIC compiler, with syntax similar to MS-QuickBASIC, that adds new features such as pointers, unsigned data types, inline assembly, object orientation, and many others.
Amulet is a Lua-based toolkit for experimenting with interactive graphics and audio. It provides a cross-platform API for drawing graphics, playing audio and responding to user input, and a command-line interpreter for running Amulet scripts.
A simple framework for creating VR with Lua. LÖVR projects work on Windows, macOS, and Linux. You can run the same code on an HTC Vive or an Oculus Rift, and there's even a drag and drop tool for exporting projects to WebVR.
HaxePunk is an open source framework, ported from FlashPunk, and designed to let you build your game on any platform. It provides the tools to quickly prototype ideas and the performance to make them great.