Add this as a bookmarklet (`javascript:<Paste this gist>`) to add some features to Harvest web UI

better-harvest.js

var table = document.getElementsByClassName("week-view-table")[0];
table.style.borderCollapse = "collapse"; 
var trs = document.getElementsByClassName("week-view-entry"); 
var curr_id = "0";
var curr_cum_hours = 0;
var curr_cum_mins = 0;
var total_length = trs.length;
var i = 0;
function addTotalRow(table, tr, pos, hours, mins) {
    var new_row = table.insertRow(pos+1);
    new_row.setAttribute("class", tr.getAttribute("class"));
    var tds = tr.getElementsByTagName("td");
    for (let j = 0; j < tds.length; j++) {
        var new_cell = new_row.insertCell(j);
        new_cell.setAttribute("class", tds[j].getAttribute("class"));
    };
    new_row.getElementsByTagName("td")[0].textContent = "Total for project";
    var total = `${curr_cum_hours + Math.floor(mins / 60)}:${(mins % 60).toString().padStart(2, '0')}`;
    new_row.getElementsByClassName("total")[0].textContent = total;
}
while (i < document.getElementsByClassName("week-view-entry").length) { 
    var tr = document.getElementsByClassName("week-view-entry")[i]; 
    if (tr.dataset['projectId'] != curr_id) {
        if (i > 0) {
            tr.style.borderTop = "3px solid black";
            addTotalRow(table, tr, i, curr_cum_hours, curr_cum_mins);
            total_length += 1;
            i += 1;
        };
        curr_id = tr.dataset['projectId'];
        curr_cum_hours = 0;
        curr_cum_mins = 0;
    };
    row_total = tr.getElementsByClassName("total")[0].textContent.trim();
    if (row_total != "0") {
        curr_cum_hours += parseInt(row_total.split(":")[0]);
        curr_cum_mins += parseInt(row_total.split(":")[1]);
    };
    i += 1;
};
addTotalRow(table, tr, i, curr_cum_hours, curr_cum_mins);
document;