Open-surface digital microfluidics refers to droplet manipulations in an open surface. Different chemical/
biological reaction protocols can easily be demonstrated in the same device by reprogramming the order of droplet
manipulations. While continuous-flow or liquid-plug microfluidics within microchannels have inherently limited programmability,
there is no limit of reprogrammability in open-surface digital microfluidics. Three different mechanisms for
droplet manipulations are addressed in this mini-review: electrowetting-on-dielectric, magnetofluidics and wire-guide
manipulations. Brief theories of surface tension and work of adhesion are addressed. Potential applications are addressed
as well as their complications.