As can be cited in the paper Field Experiments (Harrison and List, 2004 JEL). Field Experiments are classified into three categories. Of course, these three types are not always exclusive when trying to best fit an experiment.
Identical to convential lab experiments but with a non-standard subject pool. For example, running Peruvian borrowers through labs games (Karlan, 2005 AER).
Identical to artefacutal field experiments but with field context in either the commodity, task, or information set that the subjects use. For example, work that elicits valuations for publics goods that occur naturally in the environment of the subjects.
Identical to framed field experiments except that the subjects do not know they are participants in an experiment. For example, see List and Lucking-Reiley 2002 JPE paper on fundraising experiments.