Twinkle Twinkle Little Star

QBasic (56)

A$="CCGGAAG2FFEEDDC2"
B$="GGFFEED2"
PLAY "L4"+A$+B$+B$+A$

Focus is on reminiscence :)

(Don't have a QBasic to test this though)

JavaScript (214 212 211 characters)

Open Safari, Opera, or Google Chrome to JavaScript Shell, then enter the code below:

for(s="",y=192e3;x=--y/4e3|0;)s+="~ "[(y%4e3>800|x%8==1)&Math.pow(2,"024579702457245702457970"[x>>1]/12)*y/31%2];open("data:audio/wav;base64,UklGRiXuAgBXQVZFZm10IBAAAAABAAEAQB8AAEAfAAABAAgAZGF0YQHuAgCA"+btoa(s))

Unminified for readability (even then it may be hard to understand):

for(s = "", y = 192E3; x = --y / 4E3 | 0;) {
  s += "~ "[(y % 4E3 > 800 | x % 8 == 1) & Math.pow(2, "024579702457245702457970"[x >> 1] / 12) * y / 31 % 2];
}
open("data:audio/wav;base64,UklGRiXuAgBXQVZFZm10IBAAAAABAAEAQB8AAEAfAAABAAgAZGF0YQHuAgCA" + btoa(s));

With several more characters, it could work on Firefox as well, but you can change the audio/wav part to at least save the WAV file.

C# (Length: LOL)

So, what I did here was implement support for generating a .wav file from the string used for the QBasic solution in C# (single octave, no accidentals). Emphasis was on:

1. Avoiding unsafe code blocks
2. Not wasting too much of my time doing it
3. Making it relatively simple to extend

---

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text.RegularExpressions;
using System.IO;

namespace ConsoleApplication1
{
    public static class Extension
    {
        public static byte[] ToByteArray(this object o)
        {
            return o.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance)
                .SelectMany(x =>
                                {
                                    var value = x.GetValue(o, null);
                                    if (value.GetType().Equals(typeof (UInt16)))
                                    {
                                        return BitConverter.GetBytes((UInt16) value);
                                    }
                                    if (value.GetType().Equals(typeof (UInt32)))
                                    {
                                        return BitConverter.GetBytes((UInt32) value);
                                    }
                                    if (value.GetType().Equals(typeof(char[])))
                                    {
                                        return ((char[]) value).Select(y => Convert.ToByte(y));
                                    }
                                    if (value.GetType().Equals(typeof(byte[])))
                                    {
                                        return (byte[]) value;
                                    }
                                    throw new NotImplementedException();
                                }).ToArray();
        }
    }
    public class Wave
    {
        public readonly byte[] WavFile; 

        public Wave(string notes)
        {
            var header = new Header();
            var data = new List<Chunk>();
            var f = new Fmt(8000);
            data.Add(f);
            data.Add(new WavData(notes, f));
            var thefile = data.SelectMany(x => x.ToByteArray()).ToArray();
            header.Size = (uint)thefile.Length + 4;
            WavFile = header.ToByteArray().Concat(thefile).ToArray();
        }
        class WavData: Chunk
        {
            private static IEnumerable<byte> RenderNote(string note, int length, Fmt fmt)
            {
                double frequency;
                switch (note)
                {
                    case "A":
                        frequency = 440;
                        break;
                    case "B":
                        frequency = 493.883;
                        break;
                    case "C":
                        frequency = 261.626;
                        break;
                    case "D":
                        frequency = 293.665;
                        break;
                    case "E":
                        frequency = 329.628;
                        break;
                    case "F":
                        frequency = 349.228;
                        break;
                    case "G":
                        frequency = 391.995;
                        break;
                    default:
                        throw new NotImplementedException("Unsupported Note");
                }
                var result = new byte[fmt.SampleRate / length * 2];  // For 120BPM tempo
                for (int i = 0; i < result.Length; i++)
                {
                    double time = (i % fmt.SampleRate) / (double)fmt.SampleRate;
                    double position = time * frequency;
                    if (result.Length - i <= fmt.SampleRate / 16)
                        result[i] = 127;
                    else
                        result[i] = (byte)Math.Round((Math.Sin(position * 2 * Math.PI) + 1) * 127);
                }
                return result;
            }
            public WavData(string notes, Fmt fmt)
            {
                Samples = new byte[0];
                foreach (var note in Regex.Matches(notes, @"[A-G][1|2|4|8]?").OfType<Match>().Select(x => x.Value))
                {
                    Samples = Samples.Concat(RenderNote(note[0] + "", note.Length > 1 ? note[1] - '0' : 4, fmt)).ToArray();
                }

            }
            public override char[] Id
            {
                get { return "data".ToCharArray(); }
            }
            public override uint DataSize
            {
                get { return (uint)Samples.Length; }
            }
            public byte[] Samples { get; private set; }
        }
        class Fmt : Chunk
        {
            public Fmt(UInt32 sampleRate)
            {
                CompressionCode = 1; // Unknown/PCM
                Channels = 1;
                SampleRate = sampleRate;
                SignificantBits = 8;
            }
            public override char[] Id
            {
                get { return "fmt ".ToCharArray();}
            }
            public override uint DataSize
            {
                get { return 16; }
            }
            public UInt16 CompressionCode { get; private set; }
            public UInt16 Channels { get; private set; }
            public UInt32 SampleRate { get; private set; }
            public UInt32 AvgBytesPerSecond { get { return SampleRate*BlockAlign; } }
            public UInt16 BlockAlign { get { return (UInt16) (SignificantBits/8*Channels); } }
            public UInt16 SignificantBits { get; private set; }
        }
        class Header
        {
            public Header()
            {
                Type = "RIFF".ToCharArray();
                RiffType = "WAVE".ToCharArray();
                Size = 0;
            }

            public char[] Type { get; private set; }
            public UInt32 Size { get; set; }
            public char[] RiffType { get; private set; }
        }
        abstract class Chunk
        {
            public abstract char[] Id { get; }
            public abstract UInt32 DataSize { get; }
        }
    }
    class Program
    {
        public static void Main(string[] args)
        {
            var p1 = "CCGGAAG2";
            var p2 = "FFEEDDC2";
            var p3 = "GGFFEED2";
            var w = new Wave(p1+p2+p3+p3+p1+p2);
            using (var f = new FileStream("testfile.wav", FileMode.Create))
                f.Write(w.WavFile, 0, w.WavFile.Length);
        }
    }
}