Natron is a visual effects composition software. It supports many common image file formats (EXR, DPX, TIFF, JPEG, PNG); colorspace management via OpenColorIO, and visual effects via OpenFX / OFX plugins. It has low hardware requirements that allow real-time playback, comes with command line tools, and uses Python3 for scripting.
Calf Studio Gear is a stack of audio effect plugins for JACK sound servers and LV2 hooks. It contains instruments and tone generators, dynamic processors, digital effects, modulators, filters and equalizers, delay effects, distortion and enhancement filters, as well as some tools aimed at professionals.