iZotope Vocal Doubler
iZotope Vocal Doubler is a free plug-in designed to support your vocal with a natural doubling effect, adding rich tone and depth.
Vocal Doubler is perfect for placing directly on your vocal track and just adding a touch of space to make it stand out in the mix.
Using “Effect Only” mode, you can also create multiple doubled vocals on different tracks to further customize your sound.
This is a good plugin that has a nice visualisation interface. It sounds natural without metallic sounding or phase artifacts.