Obsidian

FFmpeg is the open-source command-line toolkit that decodes, converts, and processes virtually every audio and video format in existence, and quietly powers much of the internet's media infrastructure. Owning it means never needing a sketchy online converter or paid export feature. It is command-line only, so there is a real learning curve.

Godot is a free, open-source game engine for 2D and 3D games with its own scripting language, visual editor, and export to desktop, mobile, and web. There are no royalties, license fees, or runtime tracking, and the engine source is yours to modify. Its 3D capabilities and console support trail Unity and Unreal.

KiCad is a free, open-source suite for electronics design: schematic capture, PCB layout, and 3D board preview, with no license cost or board-size limits. It lets hobbyists and small companies design real hardware without renting proprietary EDA software. Some advanced features of high-end commercial tools, like autorouting and simulation depth, are weaker.

Blender is a free, open-source 3D creation suite covering modeling, sculpting, animation, rendering, simulation, and video editing, used in real film and game production. It puts a full professional 3D pipeline on your own machine with no license server or subscription. The learning curve is steep and serious work demands capable hardware.