Reactive web UIs, written in C#.

public class Counter : BaseComponent<NoProps, NoEvents, NoSlots, NoExpose>
{
    protected override IComponent[] Setup(out NoExpose exposed)
    {
        exposed = default;

        // Runs once. From here on, only what reads a signal updates.
        var count = new Signal<int>(0);
        var doubled = new Computed<int>(() => count.Value * 2);

        return
        [
            new Button
            {
                Props = new ButtonProps(),
                Events = new ButtonEvents { OnClick = _ => count.Value++ },
                Children = [new DomText { Text = "Click me".ToConstSignal() }],
            },
            new P
            {
                Props = new PProps(),
                Children = [new DomText { Text = new Computed<string>(
                    () => $"{count.Value} × 2 = {doubled.Value}") }],
            },
        ];
    }
}