One of my friend told me about tubemate.
Tubemate apps is not available on google play store.
TubeMate, would want to be on google play store but since Youtube is owned by google, it is not legal to download videos from Youtube. You can save videos offline from Youtube app itself.
You can download all kind of videos or movies in any of the quality.TubeMate is a safe app but be careful not to provide them any personal information just for security purpose.
The thing I didn't liked about tubemate is that there are very less updates of this app till date.
Rest the app is very good to use.
