I really like Twinkly lights. You can 3D map lights on the christmas tree with your phone and then play with individually controllable RGBW light points. They are relatively cheap, even non-DIY people can buy and use them. It would be great if they provided some official API, but if you want to hack them, there are ways to do it: https://labs.f-secure.com/blog/twinkly-twinkly-little-star/
