SimpleScalar - A system software infrastructure used to build modeling applications for program performance analysis, detailed microarchitectural modeling, and hardware-software co-verification.
FeS2 - A timing-first, multiprocessor, x86 simulator, implemented as a module for Virtutech Simics
GEMS - General Execution-driven Multiprocessor Simulator, based on Simics
M5 - A modular platform for computer system architecture research, encompassing system-level architecture as well as processor microarchitecture. Supports Alpha, SPARC, MIPS, and ARM ISAs, with x86 support in progress.
PTLsim - A cycle accurate out of order microprocessor simulator and virtual machine for the x86 and x86-64 instruction sets. PTLsim models a modern speculative out of order x86-64 compatible processor core, cache hierarchy and supporting hardware.