Cherry Audio has some interesting virtual modular synthesizers. And now they give away the Nucleus for FREE. A great way to start playing with virtual modules.

Tricent mk III of Full Bucket is a fantastic simulation of the Korg Trident. Great sounds and some interesting features, all packed in a free VST plugin.

Roland Zenbeats is a new Music Creation app that runs on almost all devices. A great tool to capture your creativity and make your own music anywhere.