Looking for "DJ" music software

Long story short my wedding is less then a month and a half away. We had a DJ lined up and they fell off the face of the earth. We have tried nearly everything to get a new DJ but everyone is booked.

After a ton of taking with my fiance we are making a playlist and going to have a friend act as a DJ for the day.

I am not looking for anything special. Just something that can do some smooth transitions between tracks. (Song starts to quiet as the next song overlaps and gets louder). Able to select the next song in case we want a song sooner rather then later would be a bonus.

I already have equipment for the occasion I just want a music app that is better then my stock music player.

Thank you for your time.