List all contexts and get settings with XPDO

<?php
$contexts = $modx->getCollection('modContext', array('key:NOT IN' => array('web', 'mgr')));
foreach ($contexts as $context) {
    $listContext .= "<li>" . $context->get('key') . "</li>";
}

return $listContext;

$context = $modx->getObject('modContext','web');
$settings = $context->getMany('ContextSetting');
foreach ($settings as $setting) {
    echo 'Setting name: '.$setting->get('key').' <br />';
    echo 'Setting value: '.$setting->get('value').' <br />';
}

$contexts = array(
     'context1',
     'context2',
     'context3',
);

foreach ($contexts as $context) {
    $settings = $modx->getcollection('modContextSetting',
        array(
            'context_key' => $ctx,
        )
    );
    echo '____________________________________<br />';
    echo 'Context: ' . $context->get('key') . '<br />';
    foreach ($settings as $setting) {
        echo '    Setting name: ' . $setting->get('key') . '<br />';
        echo '    Setting value: ' . $setting->get('value') . '<br />'; 
    }

}

<?php
        $contexts = array();
        /** @var modContext $contextsGraph */
        $query = $modx->newQuery('modContext');
        $query->where(array('modContext.key:NOT IN' => array('web', 'mgr', 'backup')));
        $query->sortby($modx->escape('modContext') . '.' . $modx->escape('key'), 'ASC');
        $contextsGraph = $modx->getCollectionGraph('modContext', '{"ContextSettings":{}}', $query);
        foreach ($contextsGraph as $context) {
            $contextSettings = array();
            foreach ($context->ContextSettings as $cSetting) {
                $contextSettings[$cSetting->get('key')] = $cSetting->get('value');
            }
            foreach ($contextSettings as $key => &$value) {
                $matches = array();
                if (preg_match_all('/{(.+)?}/', $value, $matches)) {
                    foreach ($matches[1] as $settingKey) $value = str_replace('{' . $settingKey .'}', $modx->getOption($settingKey), $value);
                }
            }
            $contexts[$context->get('key')] = $contextSettings;
        }

<li><a href="(site start value)">Some context</a></li>

<li><a href="[[~[[getContextSetting? &context=`someContext` $setting=`site_start`]]]]">Some context</a></li>

[[getContextSetting? &context=`myContext`, $setting=`site_start`]]