I use WDL-OL. It has templates for VST2, VST3, RTAS, AAX, standalone app, AU (Mac only). I added MIDI-FX for Logic which is basically AU with slightly different options.
Another thing I don't yet understand - are there any VST's compiled for Linux? Like for Mac - it is VST as well, but compiled with Xcode c compiler and it uses OS X Cocoa framework for GUI stuff. So code-wise core part is the same, but GUI part is different.