SoftWire was the precursor to TransGaming's SwiftAsm. SwiftAsm is an optimizing run-time x86 assembler that can be used as a JIT compiler back-end for scripting languages, or for dynamic code generation of efficient processing pipelines.
Decafcc is a simple just-in-time (JIT) compiler for small programming or data modeling language. The current Decaf project demonstrates how to parse simple C, and how to generate MIPS assemble code.