To begin with, here is what is written on the english website :
Alchemy is an open drawing project aimed at exploring how we can sketch, draw, and create on computers in new ways. Alchemy isn’t software for creating finished artwork, but rather a sketching environment that focuses on the absolute initial stage of the creation process. Experimental in nature, Alchemy lets you brainstorm visually to explore an expanded range of ideas and possibilities in a serendipitous way.
Here for an exemple :
And here goes what I can do with Alchemy. I think it is a GREAT error to put it just after the video of a professional, but I still hope to improve with time ^^.