and if yes, where it could be found?! According to this infoq entry, they have opensourced it. But right now, there is not such a product in their website.
This page, http://terracotta.org/dl/oss-download-catalog , has the links to the opensource version of terracotta and related products. You may be presented with a page requiring you to register prior to the download. I tried downloading from there yesterday, and I was able to successfully download terracotta and get it running locally.