Miracle C Compiler  
   Runs under Windows 98/ME/2000/XP and compiles for DOS box/console. Provides a multi-window development environment with integrated compiler and linker.
   http://www.c-compiler.com/

Dunfield Development Systems  
   Makers of freeware Micro-C compiler for DOS.
   http://www.dunfield.com/

TenDRA  
   The home of the open source TenDRA C/C++ compiler. [Open source, BSD]
   http://www.tendra.org/

lcc  
   Retargetable ANSI C compiler for ALPHA, SPARC, MIPS R3000, Intel x86.
   http://www.cs.princeton.edu/software/lcc/

Freeware for Solaris  
   precompiled Gnu C and C++ binaries for Solaris, for Sparc and Intel architectures.
   http://www.sunfreeware.com/

Mix Software Inc  
   Makers of Power C for DOS, Win32, and Linux. C++ addons, but no compiler
   http://www.mixsoftware.com/

SCORE  
   (Safety Critical Object-oriented Real-time Embedded) ANSI C Cross Compiler for embedded PowerPC provides a complete high quality C development environment which is based on ANDF (Architectural Neutral Distribution Format) technology.
   http://www.ddci.com/products_SCORE_ANSI_C.shtml

LCC-Win32  
   A compiler system for Windows 95 - NT, includes lcc, a development environment, and other tools.
   http://www.cs.virginia.edu/~lcc-win32/

StackGuard Compiler: a gcc Enhancement  
   Patch for GNU gcc compiler, version 2.7.2.3. For most uses, it is a drop-in replacement for a standard gcc 2.7.2.3. Linux source and binaries available.
   http://www.cse.ogi.edu/DISC/projects/immunix/StackGuard/compiler.html

Ch  
   A superset of C interpreter by SoftIntegration, Inc. It is the most complete C interpreter and an alternative to C compiler.
   http://www.softintegration.com/

Development Assistant for C  
   IDE for Embedded Software development in ANSI C. Editor, Browser, Call-Hierarchy Graph, Software Metrics, Makefile Generator, Tool Integration. Interface to Debuggers and Version Control Systems.
   http://www.ristancase.com/dac/v40/

MCPP  
   A portable C/C++ preprocessor supporting several compiler-systems on UNIX and DOS/Windows. MCPP supports C99 and C++98 as well as C90 and it provides Validation Suite which tests C/C++ preprocessor comprehensively.
   http://www.m17n.org/mcpp/index_eng.html

Pelles C  
   A complete IDE and development kit for Windows and Pocket PC. The compiler is based on LCC, and the install builder for Windows is based on NSIS. Both are heavily modified.
   http://www.smorgasbordet.com/pellesc/

Unicals Group  
   A vendor of C/C++ development tools for OEM market.
   http://www.unicals.com/

TinyCC-Win32  
   The small and fast C compiler usable as a library or exe. For I386 primarily. It also include linker and assembler. [Open source, LGPL]
   http://tinycc-win32.sourceforge.net/

Sun Studio C/C++/Fortran Compilers  
   Resources for developers using C, C++, or Fortran.
   http://developers.sun.com/prodtech/cc/

Tiny C Compiler  
   Small compiler generating optimized x86 code.
   http://fabrice.bellard.free.fr/tcc/

Open Watcom  
   Open Source project to maintain and enhance the Watcom C, C++ and Fortran Compilers.
   http://www.openwatcom.org/