There are a few plugin formats
1. VST2[2] by Steinberg, deprecated
2. VST3[3] by Steinberg, Steinberg's intended replacement for VST2
1. AU[a] by Apple, a plugin format only for [Macs](/aw/os/macos) and largely only for [Logic](/aw/music/daw/logic) and [Garageband](/aw/music/daw/garageband)
3. CLAP[c] -- a new format developed by [Bitwig](/aw/music/daw/bitwig) and [U-He](/aw/music/plugins/UHe)
4. LV2 -- a plugin format originally written for [Linux](/aw/os/linux), to supersede DSSI and LADSPA.
5. LADSPA (Linux Audio Developers Simple Plugin Api) and DSSI (Disposable Soft Synth Interface)