Here are two wonderful videos from Tokyo-based DESIGNERS APARTMENT (Takeshi Tsunehashi / 常橋岳志)
The first (above) is called "forest". Tsunehashi used Trapcode Particular for the particles and Trapcode Form for the fog. There is also a Japanese version.
"aiiro" uses Trapcode Particular for the particles.
Takeshi Tsunehashi's website: d-apartment.net