Show remaining hours for each team member on Kanban page of Redmine Backlogs plugin. Works as a Chrome user script.

remaining.user.js

(function () {
  if (location.href.indexOf('taskboards') === -1) return;

  showResult(accumulateHours());
  hookTaskRefreshed();

  function hookTaskRefreshed() {
    window.addEventListener('message', function (e) {
      if (e.data.type === 'task:refreshed') showResult(accumulateHours());
    });
    injectScript("RB.Task.refreshed = function () { window.postMessage({ type: 'task:refreshed' }, '*'); };");
  }

  function accumulateHours() {
    var tasks = Array.prototype.slice.call(document.querySelectorAll('.task'));
    return tasks.map(function (task) {
      return {
        userName: task.querySelector('.assigned_to_id .t').innerText,
        hours: parseFloat(task.querySelector('.remaining_hours').innerText) || 0
      }
    }).reduce(function (acc, task) {
      acc[task.userName] = (acc[task.userName] || 0) + task.hours;
      return acc
    }, {});
  }

  function showResult(userHours) {
    var texts = [];
    var totalHours = 0;
    for (var userName in userHours) {
      texts.push((userName || '（全体）') + ': ' + userHours[userName] + ' 時間');
      totalHours += userHours[userName];
    }
    texts.sort();

    var boxId = 'remaining-hours-summary';
    var box = document.getElementById(boxId);
    if (box) {
      box.innerHTML = '';
    } else {
      box = createBox();
      box.id = boxId;
      document.getElementById('taskboard').appendChild(box);
    }
    box.appendChild(createHeading());
    box.appendChild(createList(texts));
    box.appendChild(createTotal(totalHours));
  }

  function createBox() {
    var box = document.createElement('div');
    applyStyles(box, {
      width: '150px',
      position: 'absolute',
      top: '0px',
      right: '20px',
      zIndex: '300',
      backgroundColor: '#fcfcfc',
      padding: '7px 10px',
      border: '1px solid #ccc',
      opacity: '0.8',
      borderRadius: '3px'
    });
    return box;
  }

  function createHeading() {
    var heading = document.createElement('h4');
    heading.innerText = '残り時間';
    applyStyles(heading, {
      marginBottom: '5px'
    });
    return heading;
  }

  function createTotal(totalHours) {
    var total = document.createElement('p');
    total.innerText = '計 ' + totalHours + ' 時間';
    applyStyles(total, {
      borderTop: '1px dotted #bbb',
      textAlign: 'right',
      margin: '5px 0 0',
      padding: '5px 0 0'
    });
    return total;
  }

  function createList(texts) {
    var ul = document.createElement('ul');
    texts.forEach(function (text) {
      var li = document.createElement('li');
      li.innerText = text;
      ul.appendChild(li);
    });
    applyStyles(ul, {
      margin: '0',
      padding: '0',
      listStyleType: 'none',
      textAlign: 'right'
    });
    return ul;
  }

  function injectScript(scriptContent) {
    var script = document.createElement('script');
    script.textContent = scriptContent;
    document.head.appendChild(script);
  }

  function applyStyles(elem, styles) {
    for (var k in styles) {
      elem.style[k] = styles[k];
    }
  }
})();