Blender's interface, for your app.

import blenderui.tksyntax as tk
from blenderui.tksyntax import ttk, messagebox

root = tk.Tk()
name = tk.StringVar(value="Cube")
ttk.Entry(root, textvariable=name).pack(fill="x", padx=8, pady=8)
ttk.Button(root, text="Greet",
           command=lambda: messagebox.showinfo("Hi", "Hello " + name.get())).pack()
root.mainloop()

from blenderui.qtsyntax import (QApplication, QMainWindow, QWidget, QVBoxLayout,
                                QFormLayout, QLineEdit, QSlider, QProgressBar, Qt)

app = QApplication([])
win = QMainWindow()
central = QWidget()
layout = QVBoxLayout(central)

form = QFormLayout()
level = QSlider(Qt.Horizontal)
level.setRange(0, 100)
bar = QProgressBar()
level.valueChanged.connect(bar.setValue)   # signals connect to any callable
form.addRow("Name:", QLineEdit())
form.addRow("Level:", level)
form.addRow("Progress:", bar)
layout.addLayout(form)

win.setCentralWidget(central)
win.show()
app.exec()

use blenderui::prelude::*;

struct Hello;

impl Render for Hello {
    fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
        rsx! {
            <body m-0 p-6 flex flex-col gap-4 bg-zinc-900 text-white>
                <h1 text-2xl font-bold>"Hello, BUI"</h1>
                <NumberSlider min={0.0} max={10.0} value="5" />   // a real Blender slider
            </body>
        }
    }
}

fn main() {
    Application::new().run(|cx| {
        cx.open_window(WindowOptions::default(), |_, cx| cx.new(|_| Hello)).unwrap();
    });
}

impl Render for Settings {
    fn render(&mut self, window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
        let field = |label: &'static str| {
            div().flex().items_center().gap(px(8.0))
                .child(div().w(px(70.0)).text_color(rgb(0xb8b8b8)).child(label))
                .child(div().flex_1().h(px(20.0)).px(px(6.0)).rounded(px(4.0)).bg(rgb(0x1d1d1d))
                    .border_1().border_color(rgb(0x3d3d3d)).text_color(rgb(0xe6e6e6)).child("Cube"))
        };
        div()
            .size_full().flex().flex_col().gap(px(8.0)).p(px(12.0))
            .bg(rgb(0x303030)).text_color(rgb(0xe6e6e6)).text_size(px(13.0))
            .child(div().text_size(px(16.0)).child("Settings"))
            .child(field("Name"))
            .child(div().w(px(80.0)).h(px(22.0)).rounded(px(4.0)).bg(rgb(0x545454))
                .flex().items_center().justify_center().child("Apply"))
    }
}

use blenderui::prelude::*;

struct Todo { items: Vec<String>, draft: String }

impl Render for Todo {
    fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
        div().p_4().flex().flex_col().gap_2()
            .child(h2().child(format!("{} items", self.items.len())))
            .child(ul().children(self.items.iter().map(|s| li().child(s.clone()))))
            .child(div().flex().gap_2()
                .child(input().id("draft").placeholder("New item").value(self.draft.clone())
                    .on_change(cx.listener(|this, e: &ChangeEvent, _, cx| {
                        this.draft = e.value.clone();
                        cx.notify();
                    })))
                .child(button().child("Add").on_click(cx.listener(|this, _, _, cx| {
                    this.items.push(std::mem::take(&mut this.draft));
                    cx.notify();
                }))))
    }
}

/** @jsxImportSource @blender-ui/react */
import { render, useState, NumberSlider } from "@blender-ui/react"

function Counter() {
  const [count, setCount] = useState(0)
  return (
    <main styled className="p-6 flex flex-col gap-3">
      <span>Clicks: {count}</span>
      <button onClick={() => setCount((c) => c + 1)}>Add one</button>
      <NumberSlider min={0} max={10} />
    </main>
  )
}

render(<Counter />, { title: "Counter", width: 360, height: 200, gpu: true })

const { App, signal } = require('@blender-ui/native')

const app = new App({ gpu: true })
const win = app.window({ title: 'Hello', width: 360, height: 220 })
win.body.setAttribute('styled', '') // Blender's look for the page
win.body.className = 'm-0 p-6 flex flex-col gap-3 bg-[#2b2b2b] text-[#e6e6e6]'

const clicks = signal(0)
const label = win.createElement('span')
label.textContent = clicks // bound: follows the signal
const button = win.createElement('button')
button.textContent = 'Add one'
button.addEventListener('click', () => clicks.value++)
win.body.appendChild(label)
win.body.appendChild(button)

#include "imgui.h"
#include "imgui_impl_bui.h"

static void frame(void*) { ImGui::ShowDemoWindow(); }

int main() {
  ImGui::CreateContext();
  ImGui_ImplBUI_App* app = ImGui_ImplBUI_CreateApp("Dear ImGui on BUI", 1280, 800, frame, nullptr);
  ImGui_ImplBUI_RunApp(app);       // BUI's message loop until the window closes
  ImGui_ImplBUI_DestroyApp(app);
  ImGui::DestroyContext();
}

#include "cimgui.h"
#include "cimgui_impl_bui.h"

static void frame(void* user)
{
    float* value = (float*)user;
    ImGui_ShowDemoWindow();
    ImGui_Begin("Hello");
    ImGui_SliderFloat("Value", value, 0.0f, 1.0f);
    ImGui_Text("%.2f", *value);
    ImGui_End();
}

int main(void)
{
    float value = 0.5f;
    ImGui_CreateContext();
    cImGui_ImplBUI_App* app = cImGui_ImplBUI_CreateApp("Hello", 1280, 800, frame, &value, NULL);
    cImGui_ImplBUI_RunApp(app);
    cImGui_ImplBUI_DestroyApp(app);
    ImGui_DestroyContext();
}

import blenderui.imgui as imgui

state = {"value": 0.5}

def frame():
    imgui.show_demo_window()
    imgui.begin("Hello")
    _, state["value"] = imgui.slider_float("Value", state["value"], 0.0, 1.0)
    imgui.end()

imgui.run(frame, title="Hello", size=(1280, 800))

use blenderui_imgui as imgui;

fn main() {
    let mut value = 0.5f32;
    imgui::run("Hello", [1280, 800], move || {
        imgui::show_demo_window();
        imgui::begin("Hello");
        imgui::slider_float("Value", &mut value, 0.0, 1.0);
        if imgui::button("Reset") {
            value = 0.5;
        }
        imgui::text(&format!("value {value:.2}"));
        imgui::end();
    });
}

#include "BUI_kit.h"

int main(void)
{
  BKNode *root = BK_node_new("frame");
  BKNode *size = BK_node_new("slider");
  BK_set_str(size, "label", "Size");
  BK_set_num(size, "max", 10);
  BK_set_num(size, "value", 2.5);
  BK_node_add(root, size, -1);              /* -1: append */
  BK_geom_set_manager(size, BK_GEOM_PACK);  /* Tk's packer */

  BKContext *ctx = BK_context_new(root);
  BKHost host = {0};                        /* the window fills it in */
  BK_context_set_host(ctx, &host);
  BKWindow *win = BK_window_new(ctx, "BUI from C", 320, 120);
  BK_window_show(win);
  BK_window_run();
  return 0;
}