Twig Calendar in divs format because tables are hard for responsive. Don't remember where I got this from originally, so if you know or see it let me know and I'll attribute.

calendar.twig

{#
 Creates a faux table twig calendar.
 
 Takes the following variables:
   month
   currentDay
   calendarContent
 
 month can be any string acceptable by http://www.php.net/strtotime, the
 template will output that time's month.
 If you don't want to pass in a date you can set time like this:
 {% set month = "now"|date("U") %}
 {% set month = "December 2012"|date("U") %}
 
 currentDay is an integer of the current day, 1-31.
 
 How ever you want to output items onto the calendar is a different issue,
 but I'd assume pushing everything into an array numerically indexed by that day:
 $calendarContent = array(1=>array('Something on the first'),31=>array('Halloween'));
#}
<div class="calendar">
    <div class="calendar__header">
        <div class="calendar__title">
            {{ month|date('F Y') }}
        </div>
        <div class="calendar__row">
            <div class="calendar__day calendar__heading">S<span class="calendar__heading--abbr">un</span><span class="calendar__heading--full">day</span></div>
            <div class="calendar__day calendar__heading">M<span class="calendar__heading--abbr">on</span><span class="calendar__heading--full">day</span></div>
            <div class="calendar__day calendar__heading">T<span class="calendar__heading--abbr">ue</span><span class="calendar__heading--full">sday</span></div>
            <div class="calendar__day calendar__heading">W<span class="calendar__heading--abbr">ed</span><span class="calendar__heading--full">nesday</span></div>
            <div class="calendar__day calendar__heading">T<span class="calendar__heading--abbr">hu</span><span class="calendar__heading--full">rsday</span></div>
            <div class="calendar__day calendar__heading">F<span class="calendar__heading--abbr">ri</span><span class="calendar__heading--full">day</span></div>
            <div class="calendar__day calendar__heading">S<span class="calendar__heading--abbr">at</span><span class="calendar__heading--full">urday</span></div>
        </div>
    </div>
    <div class="calendar__body">
        <div class="calendar__row">
        {% set daysInMonth = month|date('t') %}
        {% set startDow = month|date('F 1\\s\\t Y')|date('w') %}
        {% set dow = startDow %}
        {% for day in range(1,daysInMonth) %}
            {% if loop.first and startDow != 0 %}
                <div class="calendar__span calendar__begin calendar__span--spans-{{ startDow }}"></div>
            {% endif %}
            <div class="calendar__day {% if (currentDay | date('j')) == day %}calendar__day--current{% endif %}">
                <div class="calendar__number">{{ day }}</div>
                <div class="calendar__day-content">
                    {{ calendarContent[day] }}
                </div>
            </div>
            {% if loop.last and dow != 6 %}
                <div class="calendar__span calendar__span--spans-{{ 6 - dow }}">&nbsp;</div>
            {% endif %}
            {% if dow == 6 %}
            {% set dow = 0 %}
        </div>
        <div class="calendar__row">
            {% else %}
                {% set dow = dow + 1 %}
            {% endif %}
        {% endfor %}
        </div>
    </div>
</div>