A round Windows Form that moves along the mouse when pressed. Based on my previous gist: https://gist.github.com/georgw777/8900639.

FormRound.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Drawing.Drawing2D;

namespace RoundForm
{
    public partial class FormRound : Form
    {
        public FormRound()
        {
            InitializeComponent();
        }

        private void FormRound_Paint(object sender, PaintEventArgs e)
        {
            // Put this in the form paint event void.
            // Create a GraphicsPath that should represent the form's shape.
            GraphicsPath formShape = new GraphicsPath();
            // Add an ellipse to the shape.
            // Any shape is valid, including rectangles, etc.
            // Check out http://msdn.microsoft.com/en-us/library/system.drawing.drawing2d.graphicspath_methods%28v=vs.110%29.aspx for all possible shapes.
            formShape.AddEllipse(0, 0, this.Width, this.Height);
            // Set this form's region parameter to the previously created GraphicsPath.
            this.Region = new Region(formShape);
        }

        private bool mouseDown = false;
        private int xDifference = 0;
        private int yDifference = 0;

        private void FormRound_MouseDown(object sender, MouseEventArgs e)
        {
            xDifference = MousePosition.X - this.Left;
            yDifference = MousePosition.Y - this.Top;
            mouseDown = true;
        }

        private void FormRound_MouseUp(object sender, MouseEventArgs e)
        {
            mouseDown = false;
        }

        private void timerMouse_Tick(object sender, EventArgs e)
        {
            if (mouseDown)
            {
                this.Left = MousePosition.X - xDifference;
                this.Top = MousePosition.Y - yDifference;
            }
        }

        private void FormRound_Load(object sender, EventArgs e)
        {
            timerMouse.Start();
        }

        private void buttonClose_Click(object sender, EventArgs e)
        {
            this.Close();
        }
    }
}