With inheritance, virtual methods, base calls, abstract and static classes

internal sealed class Student : Person
{
    public override ToString()
    {
        return base.ToString() + id;
    }
    public abstract int GetGrades();
}

Including get-only and set-only, indexers and modifiers

string this[int index] { get { return items[index].ToString(); }
int ID { get; private set; }

With multiple inheritance

public interface IStudent : IPerson, IDisposable

Generic classes, interfaces and methods with generic constraints

public class Bag<T> where T: IComparable<T>
{
    private readonly HashSet<T> items;
    public bool IsSame<U>(U key)
    {
        ...

All of C# integral types, including int, double, float, string, char, bool, uint, short, byte and more

string name = "James" + ' ' + id.ToString();
char initials = name[0];
int length = name.Length;

Sink.OnNotify += Listener_OnNotify;
Func f = IsPrime;

Student james = Array.Find(students, s => s.Name == "James");
var func = n => { string s = n + " " + "World"; Console.WriteLine(s); };
                    

Read-only structs only

Including flags enums

enum Fruits
{
  Apple,
  Banana = 1,
  Orange = Apple | Banana
}
int value = (int)Fruits.Banana;

While, for and foreach. Continue and break.

Assembly assembly = Assembly.GetExecutingAssembly();
foreach (Type type in assembly.GetTypes())
{
  foreach (MethodInfo currentMethod in type.GetMethods())
  {
    if (currentMethod.GetCustomAttributes(typeof(TestAttribute), false).Count > 0)
    {
      var instance = type.GetConstructors()[0].Invoke(new object[0]);
      currentMethod.Invoke(instance, new object[0]);
    }
  }
}

public bool TryParse(string text, out int value)

public string format(string formatstring, params object[] arguments)

public bool TryParse(string text, out int value, CultureInfo cultureInfo = null)

Including is, as, typeof

Support for async and await (partially)

try..catch, try...finally, using

Support for checked and unchecked, integer arithmetic, and bitwise operations

Resource files are automatically encoded and embedded into JS assembly file

HTMLImageElement imageElement = Properties.Resources.duocode.Image;
					
string text = Assembly.GetExecutingAssembly().GetManifestResourceString("resource.txt");

Support for nameof expression (C# 6.0)

throw new ExceptionArgument(id, nameof(id));

Support for Expression-bodied function members (C# 6.0)

public Point Move(int dx, int dy) => new Point(x + dx, y + dy); 
public void Print() => Console.WriteLine(First + " " + Last);

Support for Expression-bodied properties (C# 6.0)

public string Name => First + " " + Last; 

Support for using static (C# 6.0) to import static members of types directly into scope

using System.Console; 
using System.Math;
using DuoCode.Dom.Global;

class Program 
{ 
    static void Main() 
    { 
        WriteLine(Sqrt(3*3 + 4*4)); 
        WriteLine(navigator.userAgent); 
    } 
}