This project offers open source implementations for UNESCO/IFIP's Algol 68 (the Revised Report language).
The project offers two implementations:
Implementation 1 is Algol68G: a recent checkout hybrid compiler/interpreter by Marcel van der Veer, supporting arbitrary arithmetic, partial parametrisation, complex numbers, POSIX threads, GNU plotutils, GNU scientific library, curses, sound, TCP sockets, RegEx and PostgreSQL.
Inplementation 2 is algol68toc, a port by Sian Mountbatten of the vintage Algol68RS (UK Defense Research Agency) compiler. The implementation emits C code.
As the most popular languages of a given time continue to get worse and worse -- particularly imperative languages -- we need more well done projects like this to provide historically important languages in a usable form.
200 code samples of Algol68 are located at: http://rosettacode.org/wiki/ALGOL_68