Lisp dialect by Paul Graham; readings in: design philosophy, lessons, why it isn't especially object-oriented, FAQ. Open source, Perl Artistic License.
Page at Massachusetts Institute of Technology, Computer Science and Artificial Intelligence Laboratory (CSAIL), in the PDOS group, of main Arc coauthor. Contact information, list of publications, talks.
Lisp-like scripting language for .NET; uses Lisp dialect similar to Arc but tightly integrated with .NET Framework which has a rich set of libraries. Open source GPL.