Google Apps Script to create a digest from a set of messages in Gmail. It does a bit more than that, filters by time, strips the html, trims legalese (or whatever) and tags messages so they are not processed again. Ideal to schedule it in gmail.

gistfile1.js

function GenerateDigest() {
  //Function that goes through a search query based on time and optional label in gmail, strips html, collates into a single email, sends it to a desired address and then labels the emails as processed.
  
  
  // Where the digest email is going
  var to_emailAddress = "[email protected]"; 
  
  
  //We calculate the 24 hour range, I plan to run this every day at 9:00 to get last 24 hours of emails
  var month = new Date().getMonth();
  var date = new Date().getDate();
  var year = new Date().getFullYear();
  var time1 = new Date(year, month, date, 0, 0, 0).getTime();
  //24 hours in miliseconds
  var time2 = time1 - 86400000;
  
  // Query to select the messages to digest, tweak to select labels or origins e.g. From:
  var query = "newer:" + time2/1000 + " older:"  + time1/1000 + " in:inbox" + " -label:Digested from:[email protected]"; 
  var threads = GmailApp.search(query);
  
  
  
  var messages;
  var message;
  var date;
  var date_formatted;
  var subject;
  var body_html;
  var body_plain;
  var body_plain_excerpt;
  var digest_body;
  
    try {
    digest_body="";
    for(var t in threads) {
    
      // Get ALL the messages to each thread
      messages = threads[t].getMessages();
      startseparator = "----Start------";
      endseparator =   "------End------";
      crlf = "\n";
    
      
      for(var m in messages) {        
        message = messages[m].getBody();
        date  = messages[m].getDate();
        date_formatted = Utilities.formatDate(date, "GMT", "yyyy-MM-dd'T'HH:mm")
        subject = messages[m].getSubject();
        
        body_html = messages[m].getBody();
        
        //Google returns the body content in html, so we remove the html formatting
        body_plain= getTextFromHtml (body_html);
        body_plain_excerpt=body_plain
       
       //Optional regexp to further trim the digest, remove signature or other legalese we dont want 
           var pattern= /^(.*?)The opinions expressed in the posted.*/igm;    
           var match;        
           while ( match = pattern.exec(body_plain)) {      
            //For some reason I cannot get the subgroup capture, 
            //but I do get the match.index so for the moment it works 
            //by doing a left(). To improve here.
             body_plain_excerpt= body_plain.substring(0,match.index);
       //End of optional section
     }
       
       
       //We append the excerpt to the main digest body string, plus some header information
       digest_body = digest_body + startseparator + crlf + "Date:"+ date_formatted  + crlf + "Subject:" + subject + crlf + body_plain_excerpt + crlf+  endseparator +crlf;
        
    
     }
    }
    
    // We send the email  
    var digest_subject = "Digest of selected emails received in the last 24 hours" + Utilities.formatDate(new Date(), "GMT", "yyyy/M/d");
    MailApp.sendEmail(to_emailAddress, digest_subject, digest_body);    
    
    
    
    
    //we label the results from the query as Digested to prevent reprocessing
    //Given we rerun the exact query it shouldnt yield different, but have a look if this can be improved
    var label = GmailApp.getUserLabelByName("Digested");
    var threads = GmailApp.search(query);   
    for (var i = 0; i < threads.length; i++) {
         label.addToThread(threads[i]);
       }

   
    //
    } catch (err) {
    Logger.log("[Error Generating] getMessage: " + err);
     
    }
  Logger.log("[Success] Digest created");

}



function getTextFromHtml(html) {
  return getTextFromNode(Xml.parse(html, true).getElement());
}

function getTextFromNode(x) {
  switch(x.toString()) {
    case 'XmlText': return x.toXmlString();
    case 'XmlElement': return x.getNodes().map(getTextFromNode).join('');
    default: return '';
  }
}

More info: http://www.hongkiat.com/blog/apps-scripts-gmail-users/