Hello Chris,

There is an opened request for an Accordion style expander (Panelbar) that you can follow here to receive notification emails on status changes. I have added an additional vote on your behalf to increase the feature's priority in our back log. 

With that said, I am closing this item as a duplicate of the original Panelbar request to keep the portal clean of duplicates.

In the meantime, I will propose a couple of alternative solutions that you may try to achieve behavior similar to a Panelbar:

Using AnimationContainer component

You could make a component to achieve similar behavior through the AnimationContainer component we provide. Here's a basic example of the functionality so you can tweak it further (and, of course, expose as a stanadalone component in your app, and implement templates and so on)

<div style="position: relative; width: 400px; border: 1px solid red;">
    <div>
        <h6>Title goes here</h6>
        <span style="position: absolute; top: 0; right: 0">
            <TelerikButton Icon="@( Expanded ? IconName.ArrowChevronUp : IconName.ArrowChevronDown )"
                           OnClick="@ExpandCollapse" />
        </span>
    </div>
    <TelerikAnimationContainer @ref="@AnimContainer" Width="100%" Height="100px" Class="k-popup">
        lorem ipsum dolor sit amet
    </TelerikAnimationContainer>
</div>

@code {
    TelerikAnimationContainer AnimContainer { get; set; }
    bool Expanded { get; set; }

    async void ExpandCollapse()
    {
        await AnimContainer.ToggleAsync();
        Expanded = !Expanded;
    }
}

I have also provided another example with some custom markup that uses existing Telerik classes, and the AnimationContainer - please see the attached file PanelBarSample

Using the TreeView component

Since the TreeView offers expand/collapse animations, you can put generic content in its Template to achieve the similar to Panelbar behavior. You can find more details for the Treeview here.

Regards,
Nadezhda
Progress Telerik