In the GUI, if you right click on the tabs at the top, a menu appears with a checkbox item that says `Tabs Toolbar`. Clicking that makes the tabs at the top disappear. However there is no way for the tabs to be brought back except by restarting the software.

IMO it really isn't useful to hide the tabs and I'm not sure if there is an easy way to make a menu which brings them back.
{
    QActionGroup *tabGroup = new QActionGroup(this);
    overviewAction = new QAction(platformStyle->SingleColorIcon(":/icons/overview"), tr("&Overview"), this);
    overviewAction->setStatusTip(tr("Show general overview of wallet"));
    overviewAction->setToolTip(overviewAction->statusTip());
    overviewAction->setCheckable(true);
    overviewAction->setShortcut(QKeySequence(Qt::ALT + Qt::Key_1));
    tabGroup->addAction(overviewAction);
    sendCoinsAction = new QAction(platformStyle->SingleColorIcon(":/icons/send"), tr("&Send"), this);
    sendCoinsAction->setStatusTip(tr("Send coins to a Bitcoin address"));
    sendCoinsAction->setToolTip(sendCoinsAction->statusTip());
    sendCoinsAction->setCheckable(true);
    sendCoinsAction->setShortcut(QKeySequence(Qt::ALT + Qt::Key_2));
    tabGroup->addAction(sendCoinsAction);
    sendCoinsMenuAction = new QAction(platformStyle->TextColorIcon(":/icons/send"), sendCoinsAction->text(), this);
    sendCoinsMenuAction->setStatusTip(sendCoinsAction->statusTip());
    sendCoinsMenuAction->setToolTip(sendCoinsMenuAction->statusTip());
    receiveCoinsAction = new QAction(platformStyle->SingleColorIcon(":/icons/receiving_addresses"), tr("&Receive"), this);
    receiveCoinsAction->setStatusTip(tr("Request payments (generates QR codes and bitcoin: URIs)"));
    receiveCoinsAction->setToolTip(receiveCoinsAction->statusTip());
    receiveCoinsAction->setCheckable(true);
    receiveCoinsAction->setShortcut(QKeySequence(Qt::ALT + Qt::Key_3));
    tabGroup->addAction(receiveCoinsAction);
    receiveCoinsMenuAction = new QAction(platformStyle->TextColorIcon(":/icons/receiving_addresses"), receiveCoinsAction->text(), this);
    receiveCoinsMenuAction->setStatusTip(receiveCoinsAction->statusTip());