This package provides a comprehensive library of particle effect textures to be used with a particle system, such as Unity's particle system.
You get a huge collection of particle textures, a bunch of seamless tiling effect textures and a couple animated particle sprite sheets.
You also get a general purpose plane mesh (one and two sided versions), a couple example prefabs that use the textures from this pack and finally, theres a .ZIP package containing versions of the particle textures with a transparent background for advanced uses. Most likely, this package is compatible other particle systems outside Unity too.