LADSPALADSPA is an acronym for Linux Audio Developers Simple Plugin API. It is an LGPLd standard interface for handling filters, effectss and the like in Linux-based operating systems. It is used in many free audio software projects.
A sequel to LADSPA which is supposed to handle such things as virtual instruments (software synthesizers) is under development. It is called MAIA, the Multimedia Application Integration Architecture, which is to supply functionality equal to, for example, Steinbergs VST instruments.