Bootstrap rendering of blocks in EPiServer, with AJAX support on On Page Editing. Bootstrap.cshtml should be put in /Views/Shared/DisplayTemplates/ and don't forget to use Tag = "Bootstrap" in the page template.

bootstrap-rendering.css

/* for On Page Editing to show vertical lines when dragging/dropping */

.row > div > [data-epi-block-id] {
    float: left;
    width: 100%;
}

Bootstrap.cshtml

@model EPiServer.Core.ContentArea

@{
    new BootstrapContentAreaRenderer().Render(Html, Model);
}

BootstrapContentAreaRenderer.cs

using EPiServer.Editor;
using EPiServer.ServiceLocation;
using EPiServer.Web.PropertyControls;
using EPiServer.Web.WebControls;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using EPiServer.Core;
using System.Web.Mvc;
using EPiServer.Web.Mvc.Html;

public class BootstrapContentAreaRenderer : ContentAreaRenderer
{
    protected override void RenderContentAreaItems(HtmlHelper htmlHelper, IEnumerable<ContentAreaItem> contentAreaItems)
    {
        if (!contentAreaItems.Any())
        {
            return;
        }

        var row = new TagBuilder("div");

        row.AddCssClass("row");
        var rowWidth = 0;
            
        htmlHelper.ViewContext.Writer.Write(row.ToString(TagRenderMode.StartTag));

        foreach (var contentAreaItem in contentAreaItems)
        {
            var cell = new TagBuilder("div");
            int cellWidth;

            var displayOption = contentAreaItem.LoadDisplayOption();

            if (displayOption == null || !TryTranslateTagToColumnWidth(displayOption.Tag, out cellWidth))
            {
                cellWidth = 4;
            }

            //if (contentRenderer.CurrentData is IFullWidthBlock)
            //{
            //    cellWidth = 12;
            //}

            if (cellWidth == 3)
            {
                cell.AddCssClass("col-xs-6");
                cell.AddCssClass("col-md-3");
            }
            else if (cellWidth == 6)
            {
                cell.AddCssClass("col-xs-6");
            }
            else
            {
                cell.AddCssClass("col-sm-" + cellWidth);
            }

            if (rowWidth + cellWidth > 12)
            {
                htmlHelper.ViewContext.Writer.Write(row.ToString(TagRenderMode.EndTag));
                htmlHelper.ViewContext.Writer.Write(row.ToString(TagRenderMode.StartTag));

                rowWidth = 0;
            }

            rowWidth += cellWidth;

            htmlHelper.ViewContext.Writer.Write(cell.ToString(TagRenderMode.StartTag));
                
            RenderContentAreaItem(htmlHelper, contentAreaItem, GetContentAreaItemTemplateTag(htmlHelper, contentAreaItem), GetContentAreaItemHtmlTag(htmlHelper, contentAreaItem), this.GetContentAreaItemCssClass(htmlHelper, contentAreaItem));

            htmlHelper.ViewContext.Writer.Write(cell.ToString(TagRenderMode.EndTag));
        }

        htmlHelper.ViewContext.Writer.Write(row.ToString(TagRenderMode.EndTag));
    }

    public static bool TryTranslateTagToColumnWidth(string tag, out int columnWidth)
    {
        switch (tag)
        {
            case "half": columnWidth = 6; return true;
            case "third": columnWidth = 4; return true;
            case "twothirds": columnWidth = 8; return true;
            case "fourth": columnWidth = 3; return true;
            default: columnWidth = default(int); return false;
        }
    }
}

DisplayOptionsInitialization.cs

using EPiServer.Framework;
using EPiServer.Framework.Initialization;
using EPiServer.ServiceLocation;
using EPiServer.Web;

[InitializableModule]
[ModuleDependency(typeof(EPiServer.Web.InitializationModule))]
public class DisplayOptionsInitialization : IInitializableModule
{
    public void Initialize(InitializationEngine context)
    {
        var displayOptions = ServiceLocator.Current.GetInstance<DisplayOptions>();

        displayOptions.Add(
            id: "half",
            tag: "half",
            name: "Half"
        );

        displayOptions.Add(
            id: "third",
            tag: "third",
            name: "Third"
        );

        displayOptions.Add(
            id: "twothirds",
            tag: "twothirds",
            name: "Two thirds"
        );

        displayOptions.Add(
            id: "fourth",
            tag: "fourth",
            name: "Fourth"
        );
    }

    public void Preload(string[] parameters) { }

    public void Uninitialize(InitializationEngine context) { }
}

Page.cshtml

@using EPiServer.Core
@using EPiServer.Web.Mvc.Html

@model EPiServerSite.Models.Pages.StartPage

<html>
<head>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
    <link rel="stylesheet" href="/ClientResources/Styles/bootstrap-rendering.css">
</head>
<body>
    <div>
        @Html.PropertyFor(m => m.Blocks, new { Tag = "Bootstrap" })
    </div>
</body>
</html>