FL SynthMaker was updated to version 2 with FL Studio 10.0.9. FL SynthMaker has been included FREE with FL Studio Producer Edition (and upward) since FL Studio 8.
FL SynthMaker loads as an Instrument or Effect plugin and is an audio programming application that is used to create synth and effect plugins without the need to write programming code. The instruments and effects you create in SynthMaker can be used in FL Studio as 'native' plugins and shared with other FL Studio users. FL Synthmaker 2 loads all Synthmaker 2 projects from the stand-alone version.
Importantly FL Synthmaker comes with many pre-made synth, effect and dashboard projects, that become plugins at the click of a button, check them out here.
You can also learn more about SynthMaker 2 here.