Gargoyle Dec 11, 2010
It supports many game formats through the use of Glk.
Its most outstanding feature is its simplicity and typographical elegance.
Gargoyle is available from its website (which, as of this writing, points you to its Google Code project downloads page) for Windows and Mac. For Linux, check your distro's package repository or compile it from source. On Debian/Ubuntu, the package is gargoyle-free. (It doesn't include the non-free Alan and Hugo interpreters, and uses a free font.)