Merge tools are not detected on Mac OS X
When running TortoiseHg on OS X, when going to Settings (either Global or repository-specific), the dropdowns for "Three-way Merge Tool" and "Visual Diff Tool" are both empty, even when there are merge / diff tools available on the box, installed in the standard location (the /Applications folder).
From reviewing the source code in TortoiseHg and hglib itself, it looks like this is only built to work for Windows. It appears it uses paths and registry settings that are windows specific to discover tools, and doesn't appear to have any support for mac/linux paths / locations.
TortoiseHg/Hglib should support the detection of diff/merge tools on non-Windows platforms.