rlvm is an open source implementation of the RealLive virtual machine for Linux and OSX. RealLive is a game engine used in Japan to write visual novels, a few of which I care about, and many that I do not.
Currently, rlvm works with: Kanon Standard Edition, Air Standard Edition, CLANNAD, CLANNAD Full Voice Edition and Planetarian, along with a few non-KEY games. rlvm can optionally use English patches to some games.
In addition, English patches are supported; rlvm implements Haeleth's rlBabel extensions.