Result

横向きのフローチャートです。家系図とかにも使えそう
コードは固定的で現在の環境下ではやや汎用性に欠けるかもしれません

css

.branch {
  position: relative;
  margin-left: 250px;
}
.branch:before {
  content: "";
  width: 50px;
  border-top: 2px solid #eee9dc;
  position: absolute;
  left: -100px;
  top: 50%;
  margin-top: 1px;
}

.entry {
  position: relative;
  min-height: 60px;
}
.entry:before {
  content: "";
  height: 100%;
  border-left: 2px solid #eee9dc;
  position: absolute;
  left: -50px;
}
.entry:after {
  content: "";
  width: 50px;
  border-top: 2px solid #eee9dc;
  position: absolute;
  left: -50px;
  top: 50%;
  margin-top: 1px;
}
.entry:first-child:before {
  width: 10px;
  height: 50%;
  top: 50%;
  margin-top: 2px;
  border-radius: 10px 0 0 0;
}
.entry:first-child:after {
  height: 10px;
  border-radius: 10px 0 0 0;
}
.entry:last-child:before {
  width: 10px;
  height: 50%;
  border-radius: 0 0 0 10px;
}
.entry:last-child:after {
  height: 10px;
  border-top: none;
  border-bottom: 2px solid #eee9dc;
  border-radius: 0 0 0 10px;
  margin-top: -9px;
}
.entry.sole:before {
  display: none;
}
.entry.sole:after {
  width: 50px;
  height: 0;
  margin-top: 1px;
  border-radius: 0;
}

.label {
  display: block;
  min-width: 150px;
  padding: 5px 10px;
  line-height: 20px;
  text-align: center;
  border: 2px solid #eee9dc;
  border-radius: 5px;
  position: absolute;
  left: 0;
  top: 50%;
  margin-top: -15px;
}

特に説明は不要だと思いますので割愛します

html

<div id="wrapper"><span class="label">Root</span>
  <div class="branch lv1">
    <div class="entry"><span class="label">Entry-1</span>
      <div class="branch lv2">
        <div class="entry"><span class="label">Entry-1-1</span>
          <div class="branch lv3">
            <div class="entry sole"><span class="label">Entry-1-1-1</span></div>
          </div>
        </div>
        <div class="entry"><span class="label">Entry-1-2</span>
          <div class="branch lv3">
            <div class="entry sole"><span class="label">Entry-1-2-1</span></div>
          </div>
        </div>
        <div class="entry"><span class="label">Entry-1-3</span>
          <div class="branch lv3">
            <div class="entry sole"><span class="label">Entry-1-3-1</span></div>
          </div>
        </div>
      </div>
    </div>
    <div class="entry"><span class="label">Entry-2</span></div>
    <div class="entry"><span class="label">Entry-3</span>
      <div class="branch lv2">
        <div class="entry"><span class="label">Entry-3-1</span></div>
        <div class="entry"><span class="label">Entry-3-2</span></div>
        <div class="entry"><span class="label">Entry-3-3</span>
          <div class="branch lv3">
            <div class="entry"><span class="label">Entry-3-3-1</span></div>
            <div class="entry"><span class="label">Entry-3-3-2</span>
              <div class="branch lv4">
                <div class="entry"><span class="label">Entry-3-3-2-1</span></div>
                <div class="entry"><span class="label">Entry-3-3-2-2</span></div>
              </div>
            </div>
            <div class="entry"><span class="label">Entry-3-3-3</span></div>
          </div>
        </div>
        <div class="entry"><span class="label">Entry-3-4</span></div>
      </div>
    </div>
    <div class="entry"><span class="label">Entry-4</span></div>
    <div class="entry"><span class="label">Entry-5</span></div>
  </div>
</div>

via

CSS Horizontal Family Tree