Today I was working on one of my project and I noticed the need of selecting multiple values in a DropDownList. Being a .NET guy my first thought was to us ListBox because is gives same feature, we can selected multiple values by holding ctrl (control) key. But the reason for not using it was that it is not user friendly and its view is not good.
After searching for few minutes I found this Bootstrap Multiselect plugin. I was using bootstrap in my project as well so that was best fit for me. For other also it is very good tool and very easy to use with any platform. I used it with ASP.NET web forms so showing the same here.