Sphere 1.5/1.6b: thread (http://forums.spheredev.org/index.php/topic,155.0.html)
TurboSphere: thread (http://forums.spheredev.org/index.php/topic,13.0.html)
minisphere: thread (http://forums.spheredev.org/index.php/topic,1215.0.html)
unnamed Sphere clone in SDL: thread (http://forums.spheredev.org/index.php/topic,72.0.html)
sphere-sfml: thread (http://forums.spheredev.org/index.php/topic,137.0.html)
Sphere Web Edition: thread (http://forums.spheredev.org/index.php/topic,154.0.html)
(edit: added minisphere +neo)