T is a dialect of Scheme and its implementation. It is not compatible with R5RS, but there is an R5RS (well, currently, only R3RS) compatibility layer for it. It is planned to become more and more compatible with R5RS as time progresses. Used in the T implementation is Orbit?, an optimizing compiler, one of the first real optimizing compilers of Scheme, and for a long time the fastest. Olin Shivers wrote a detailed history of T.
T originated from Yale. Those involved in the original development of T included Jonathan Rees, Kent M. Pitman, Norman Adams, Jim Philbin, Olin Shivers, David Kranz, Richard Kelsey, and undoubtedlymore that elude this page's maintainer's memory right now. Taylor Campbell and Brian Mastenbrook, after over a decade of T's abandonment, have decided to revive the T project. (Taylor and Brian are not the original authors of T; nor were they in any way connected with the original development of T.)
Riastradh is involved with this project.
For more information about this project visit channel #t on Freenode