How to deal with module conflicts ("anti-dependencies")?
The module just needs to implement hook_requirements(); a requirement could be that a module is not installed, and if the module returnes an error from hook_requirements(), then it will not be installed.

The module should implement code similar to the following one:

function mymodule_requirements($phase) {
  $requirements = array();
  // Ensure translations don't break at install time
  $t = get_t();

  if ($phase == 'install') {
    if (module_exists('other_module')) {
      $requirements['mymodule'] = array(
        'title' =&gt; $t('My module'), 
        'value' =&gt; $t('My module is not compatible with Other module.'), 
        'severity' =&gt; REQUIREMENT_ERROR, 
      );
    }
  }

  return $requirements;
}