SLX Explorer is a flexible, retargetable version of the SLX Mapper with an user-editable abstract multicore model for hardware and software system architects. Its flexibility serves two main use cases. On one hand, it enables architects to search for the best-suited off-the-shelf multicore platform for a given application. On the other hand, it allows to perform "what if" analysis with respect to software and hardware changes to drive exploration, design, and evolution for next generation multicore systems. Examples of what-if queries include (i) analyzing the effects of hypothetical changes in the application workload due to upcoming radio or multimedia standards and (ii) analyzing the effects on application performance of adding processors, memories, and hardware accelerators onthe current multicore architecture. SLX Explorer employs Silexica's abstract platform model and proprietary parallel performance estimation technology, enabling turn-around times 2-3 orders of magnitude faster than state-of-the-art instruction-set simulators.