This is an improved and modernised version of the Algol68 mode by Jose E. Marchesi. It fully supports automatic indentation and font locking (i.e. syntax highlighting) including the three comment styles.
a68-mode supports only the UPPER stropping style and not the QUOTE or POINT style. Patch for those are welcome. At least in theory, it could be possible with a clever usage of text properties and/or overlays to implement the strict language and use a bold typeface for the "reserved words".
Just put a68-mode.el somewhere in your load-path and require it.
Or visit the file with Emacs and M-x package-install-file RET.
The following variables are available for customization:
a68-indent-level(default 3): indentation offseta68-comment-style(default"#"): the default comment style used by e.g.comment-dwim.
see M-x customize-group a68 RET for more info.
It doesn't handle well shebangs: #! is taken as the start of the
comment up to the next #.