I love World Creator, especially the vegetation distribution pipeline. You can create some very realistic fields with it. Im going to check out impostors too - ive seen it a few times and wondered what it's about.
Stupid Rental. My Zbrush that I haven't paid for an update in years and is perpetual Trumps that on all counts.
TransitionKit: Open source scene-to-scene for Unity
PaletteKit is a helpful editor used for displaying color palettes, managing and importing them. Originally its’ creators wanted to use this software with the ProBuilder program and replace it’s vertex coloring system.