Mesos is a tool to gather binary code coverage on all user-land Windows targets without need for source or recompilation. It also provides an automatic mechanism to save a full minidump of a process if it crashes under mesos. Mesos is technically just a really fast debugger, capable of handling tens of millions of breakpoints. Using this debugger, we apply breakpoints to every single basic block in a program. These breakpoints are removed as they are hit. Thus, mesos converges to 0-cost coverage as gathering coverage only has a cost the first time the basic block is hit.