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.
Seems like an interesting tool, although it relies on IDA to function properly (like so many other tools nowadays do), which can be prohibitively expensive.