Precise stimulus presentation and accurate experiment execution is essential in all areas of vision science. Here, we introduce a contribution to these requirements: FlashDot is a platform independent software for programming and performing psychophysical experiments. It provides an alternative to such popular interpreted packages and libraries as the Psychophysics Toolbox, Vision Egg, or PsychoPy, without the need of an additional interpreted programming language. FlashDot is an open source project (license: GPL) using OpenGL as a hardware interface. While it allows direct hardware access such as synchronization to the vertical blank, it remains highly portable: Reference implementations on Linux, MacOS X, and Windows are provided. FlashDot focuses on a high temporal precision for stimulus presentation and allows to check for lost frames throughout the whole experiment. Experiments can be programmed by a specific scripting language or alternatively by XML. The latter allows the application of graphical XML editors and, due to the widespread availability of XML libraries, makes it easier to automatically generate experiments using all modern programming languages as well as to control FlashDot by an external software. FlashDot combines low level commands like positioning single dots with higher level functions suitable for typical psychophysical use. In addition to graphical output control, FlashDot implements a large variety of mathematical and statistical functions ready for user implementations of online data analysis for adaptive sampling. An optional top level interpreter is provided for executing single line FlashDot commands immediately.