A plugin for Space Engineers game to allow modders to develop particles much easier.
As of SE v202 the -plugin launch arg no longer exists (official statement)
You have to install Plugin Loader and after that the Particle Editor will be in its plugins list.
Launch the game, load any offline world and press Shift+F to open the editor.
Past this you will have tooltips for everything, mentioning hotkeys and such.
There is still much to be improved so feedback and bugreports are welcome in the Issues tab.