"Leaf is a Japanese visual novel studio under the publisher Aquaplus, and has offices in Yodogawa-ku, Osaka, and Tokyo. It and its competitor Key (to which it is often compared) are the most popular and successful dedicated visual novel studios operating today.It was launched out of obscurity by its early release ToHeart. Leaf used the XviD video codec in several games: Aruru to Asobo!!, Tears to Tiara, Kusari, and ToHeart2 XRATED. Since XviD is free software, released under the GPL, Leaf was forced to release the source code to those games under the same license. One still required the game data to actually play the games with the source code. In addition, a free software engine called xlvns was developed soon after Leaf released its first three visual novels.
Source: Wikipedia, "Leaf (Japanese company)", available under the CC-BY-SA License.