GNU Lightning is a library that generates assembly language code at run time. It is very fast, making it ideal for Just-In-Time compilers, and it abstracts over the target CPU, as it exposes to the clients a standardized RISC instruction set (inspired by the MIPS and SPARC chips).
joeq is a Java 2 (JDK 1.3 and 1.4) compatible virtual machine. It is unique in that it is entirely implemented in Java, leading to greater reliability, portability, maintainability, and efficiency. It is also language-independent, so code from any supported language can be seamlessly compiled, linked, and executed dynamically.
h2incn tries to directly convert C/C++ headers to Nasm-style include files, and can be used in a makefile. It is useful if you want to use the same structures or external variable declarations in C and assembler code, and you don't want to use two separate files and update both each time you change something. It is written in a mix of C and C++ code. It currently works for simple files.