PlugSuit & Afloat: Only Mac OS X 10.5 is supported.
PlugSuit and Afloat are only supported under Mac OS X 10.5 or later versions, but not previous versions like 10.4 ("Tiger") or later major versions like 10.6 ("Snow Leopard").
Afloat 2.0 makes heavy use of 10.5 features, such as Core Animation. "Backporting" code would be very burdensome at this point. Previous versions of Afloat supported older Mac OS X versions (10.4 and 10.3.9, respectively), but major stability and functional improvements have made them obsolete. Those versions are unsupported and no longer available on the ∞labs web site.
PlugSuit 1.5 and later requires Mac OS X 10.5 or later, and are not supported by new versions of Mac OS X, including Mac OS X 10.6 "Snow Leopard". Future versions of PlugSuit may support new operating systems.