For a brief introduction to setting up and using some of the more beginner-friendly compilers and IDEs, see Using a Compiler.

Free (or with a free version)

• Ch_interpreter (http://www.softintegration.com) - The software works in Windows, Linux, Mac OS X, Freebsd, Solaris, AIX and HP-UX. The Ch Standard Edition is free for noncommercial use.
• Interactive C (http://www.botball.org/educational-resources/ic.php)
  • target platform: Handy Board (Freescale 68HC11); Lego RCX
• CINT is an interpreter for C and C++ code, included in the data-analysis package ROOT. The CINT interpreter is licensed under the X11/MIT license. ( https://root.cern.ch/drupal/content/cint ).
• PicoC is a very small C interpreter, intended for small embedded systems with very little code space or data space.
  • PicoC target platform: x86-32, x86-64, powerpc, arm, ultrasparc, HP-PA and blackfin processors; and is easy to port to new targets.
• Extensible Interactive C (EiC)
• lcc-win32 (http://www.cs.virginia.edu/~lcc-win32) - Software copyrighted by Jacob Navia. It is free for non-commercial use. Windows (98/ME/XP/2000/NT).
• GNU Compiler Collection (http://gcc.gnu.org) - GNU Compiler Collection. GNU General Public License / GNU Lesser General Public License.
  • MinGW (http://www.mingw.org/) provides GCC for Windows
• clang (LLVM) (http://clang.llvm.org/) - Almost everywhere
• Open Watcom (http://www.openwatcom.org) Open Source development community to maintain and enhance the Watcom C/C++ and Fortran cross compilers and tools. Version 1.4 released in December 2005.
  • Host Platforms: Win32 systems (IDE and command line), 32-bit OS/2 (IDE and command line), DOS (command line), and Windows 3.x (IDE)
  • Target Platforms: DOS (16-bit), Windows 3.x (16-bit), OS/2 1.x (16-bit), Extended DOS, Win32s, Windows 95/98/Me, Windows NT/2000/XP, 32-bit OS/2, and Novell NLMs
  • Experimental / Development: Linux, BSD, *nix, PowerPC, Alpha AXP, MIPS, and Sparc v8
• Tiny C Compiler (http://www.tinycc.org) - A small C compiler designed to work for slow computers with little disk space (e.g. on rescue disks).
• Portable C Compiler (http://pcc.ludd.ltu.se) - Portable C Compiler. BSD Style License(s).
• Small Device C Compiler (SDCC)
  • target platforms: Intel 8051-compatibles; Freescale (Motorola) HC08; Microchip PIC16 and PIC18.
• FpgaC. Target platform: FPGA hardware via XNF or VHDL files.
• C compilers for many digital signal processors (DSPs), many of them are free, and are listed in the comp.dsp FAQ.
• Microsoft Visual C++ (http://msdn.microsoft.com/visualc) - Free (partially limited) version available (Express|Community Edition)
• C Playground - Online C Programming IDE by Programiz - Free Online IDE to practice C Programming

Paid

• Intel C Compiler (http://software.intel.com/en-us/intel-compilers) - Windows, Linux, Mac, QNX, and embedded C/C++ compilers. Optimized for Intel 32-bit and 64-bit CPUs.
• Impulse C - Target platform: FPGA hardware via Hardware Description Language (HDL) files.