BEG is a commercial generator for compiler back ends. It reads a declarative description of a target processor (i.e. SPARC, MIPS, ARM, x86, etc.) and produces a possibly optimizing code generator in form of a C program.

A framework for building dynamically targetable compilers, assemblers and simulators for a wide variety of processor architectures. [Commercial]

Java-based BURG (code emitter generator) which can also be used as a general purpose dynamic programming engine. [Open source, Common Public License]

Helps programmers write applications that process machine code: assemblers, disassemblers, code generators, tracers, profilers, debuggers. Toolkit lets programmers encode and decode machine instructions symbolically. Encoding and decoding are automated based on compact specifications.

A library for dynamically generating machine code from within a C program. Code is generated using a generic RISC-like virtual instruction set which is then translated into native processor instructions. Currently vcode supports MIPS, SPARC, and Alpha processors.