@AttraktorRem

attraktorreminder.js

var ical = require('ical'),
  twit = require('twit'),
  Twit = new twit({
    'consumer_key': 'your_consumer_key_here',
    'consumer_secret': 'your_consumer_secret_here',
    'access_token': 'your_access_token_here',
    'access_token_secret': 'your_access_token_secret_here'
  }),
  now = new Date();

function formTweet(ev, now, i, l) {
  var tweet = '';

  if (!now) {
    //Enumerate the Events if there is more than one. e.g. (1/2)
    if (l > 1) {
      tweet += '(' + (i + 1) + '/' + l + ') ';
    }

    tweet += 'Um '

    //time in format xx:xx
    var time = ev.start.toTimeString();
    time = time.replace(/^([0-9]{2}:[0-9]{2}).*$/ig, '$1');
    tweet += time;

  } else {
    //event is starting right now.
    tweet += 'Jetzt'
  }

  tweet += ':\n';

  var desc = ev.description;
  var diff = tweet.length + 25; //25 = ellipsis + newline + twitter link length(23)
  if (diff + desc.length > 140) {
    //shorten the description if it's too long for a tweet
    desc = desc.length.substr(0, (140 - diff));
    desc += '…';
  }
  tweet += desc + '\n';

  tweet += ev.url;
  return tweet;
}

function runAtDate(date, func) {
  var now = (new Date()).getTime();
  var then = date.getTime();
  var diff = Math.max((then - now), 0);
  if (diff > 0x7FFFFFFF) //setTimeout limit is MAX_INT32=(2^31-1)
    setTimeout(function () {
    runAtDate(date, func);
  }, 0x7FFFFFFF);
  else
    setTimeout(func, diff);
}


ical.fromURL('http://wiki.attraktor.org/calendar.ics', {}, function (err, data) {
  var events = [];
  for (var k in data) {
    if (data.hasOwnProperty(k)) {
      var ev = data[k]
      if (ev.start.getDate() === now.getDate() &&
        ev.start.getMonth() === now.getMonth() &&
        ev.start.getFullYear() === now.getFullYear()
      ) {
        //event is today
        events.push(ev);
      }
    }
  }

  events.sort(function (a, b) {
    return (a.start.getTime() - b.start.getTime());
  });

  events.forEach(function (ev, i) {
    //Tweet the event when the script is called
    var tweet = formTweet(ev, false, i, events.length);
    Twit.post('statuses/update', {
      status: tweet
    }, function (err) {
      if (err) {
        console.log(err)
      }
    });

    //Tweet the event again when it's starting.
    runAtDate(ev.start, function () {
      var tweet = formTweet(ev, true);
      Twit.post('statuses/update', {
        status: tweet
      }, function (err) {
        if (err) {
          console.log(err)
        }
      });
    });
  });
});

The script that's running @AttraktorRem.
Executed via cron daily at 0:00.
Twitter API keys not included :)