This is fun. I wrote about "mashup products," products that take two forms of media to create something novel (http://ryanhoover.me/post/724469...). Weavly is very similar to an example I used, LoudGIF (http://loudgif.com/).
I like the random generator feature on Weavly, although it delivers mixed results. I'd love to see a better, mobile version of this that makes GIF + music creations fast and easy.
Product Hunt
Farmstead