Physics Central posted a great video about how droplets dance, collide, move and repel each other in an awesome symphony of movements. Surface tension on the edge of those droplets makes them interact with each other in strange ways.
Researchers Nate J Cira and Manu Prakash (Stanford) used water and propylene glycol to show that surface tension can sort different liquids automatically or cause droplets to chase one another in a circle.
Why do those droplets behave like that? Well, Physics Central explains:
When the droplets land on the glass surface, an encompassing vapor forms around the liquid droplets, creating a thin film that sticks to the glass. When one droplet encounters this film emanating from another droplet, it starts to pull toward its new neighbor due to an imbalance in surface tension. The area on the glass between the two droplets contains the thin vapor film, making it easier for the droplets to slide toward one another.