[TypeConverter(typeof(MyTypeConverter))]
public class MyClass
{
}

public class Converter : TypeConverter
{
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        if (sourceType == typeof(int)
            || sourceType == typeof(string)
            || sourceType == typeof(bool))
        {
            return true;
        }
        return base.CanConvertFrom(context, sourceType);
    }

    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
    {
        if (destinationType == typeof(int)
            || destinationType == typeof(string)
            || destinationType == typeof(bool))
        {
            return true;
        }
        return base.CanConvertTo(context, destinationType);
    }

    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
    {
        if (destinationType == typeof(int))
        {
            return 42;
        }
        if (destinationType == typeof(string))
        {
            return "String is fine for convertion";
        }
        if (destinationType == typeof(bool))
        {
            return true;
        }
        return base.ConvertTo(context, culture, value, destinationType);
    }

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        var sourceType = value.GetType();
        if (sourceType == typeof(int)
            || sourceType == typeof(string)
            || sourceType == typeof(bool))
        {
            return new Convertible() { ConvertionString = value.ToString() };
        }
        return base.ConvertFrom(context, culture, value);
    }
}

[TypeConverter(typeof(Converter))]
public class Convertible
{
    public string ConvertionString
    {
        get;
        set;
    }
}

var source = new Convertible();
var intValue = TypeDescriptor.GetConverter(typeof(Convertible)).ConvertTo(source, typeof(int));
var stringValue = TypeDescriptor.GetConverter(typeof(Convertible)).ConvertTo(source, typeof(string));
var boolValue = TypeDescriptor.GetConverter(typeof(Convertible)).ConvertTo(source, typeof(bool));
Console.WriteLine(intValue); //42
Console.WriteLine(stringValue); //String is fine for convertion
Console.WriteLine(boolValue); //True

var fromIntValue = TypeDescriptor.GetConverter(typeof(Convertible)).ConvertFrom(42) as Convertible;
var fromStringValue = TypeDescriptor.GetConverter(typeof(Convertible)).ConvertFrom("String is fine for convertion") as Convertible;
var fromBoolValue = TypeDescriptor.GetConverter(typeof(Convertible)).ConvertFrom(true) as Convertible;

Console.WriteLine(fromIntValue.ConvertionString); //42
Console.WriteLine(fromStringValue.ConvertionString); //String is fine for convertion
Console.WriteLine(fromBoolValue.ConvertionString); //True