The Amsterdam Compiler Kit is a cross-platform compiler and toolchain suite that is small, portable, extremely fast, and extremely flexible. It targets a number of low-end machines including the Z80, 8086 and 80386, but there are many other code generators available (including the pdp-11). It supports several languages, including ANSI C, Pascal and Modula-2, and contains integrated runtime libraries including a libc. While it used to be a commercial product, it has been made open source under a BSD license.

An on-line book describing the construction of a compiler translating a subset (?) of C into 68000 assembly. The compiler is written in Turbo Pascal.
See also the original site http://compilers.iecc.com/crenshaw/
This fifteen-part series, written from 1988 to 1995, is a non-technical introduction to compiler construction. You can read the parts on-line or download them in a ZIP file.

On-line editor, compiler and runtime for various languages. Although Fortran is claimed to be supported, I have not been able to run a simple program.

Blog written by Juan Jose Garcia Ripoll, maintainer of the Common Lisp implementation ECL.

Start of a series of blog articles about linkers.

Interesting work on Qi, a language based on Common Lisp which incorporates features such as (optional) type checking, pattern matching similar to those in ML and Haskell and logical programming (Prolog).

Scheme2Js is a Scheme to Javascript compiler distributed under the GPL license. While some effort has been spent on being as close as possible to R5rs, we concentrated mainly on efficiency. Usually Scheme2Js produces Javascript code, that is comparable to

Marc Feeley demonstrated how to write a simple Scheme to C compiler, in Scheme. In only 90 minutes! Presentation material (slides?), source code and video (200MB) are available.