Inkscape

When creating a custom filter from scratch most part of the filter editor is greyed out, only the ”New” button is active. It is placed at the bottom of a column which starts with filter and #.
This section of the panel enlists all the filter definitions embedded into the document.
Similar in nature to gradients or custom markers, dasharrays etc.
If a built-in filter was applied, it will show up here. Using gaussian blurs by the fill&stroke panel's slider and different blending modes are supposed to appear right after they are created here as well. However there seems to be some regression compared to 0.48 on this behave (on 0.92).
Filter defs are listed in their creating order. You can rename, delete and duplicate them, however drag&drop is not working for reorganising.