Can I manage someone elses twitter account via a twitter application?

[Terry]

I market other users twitter accounts and i was wondering if their is a twitter authorised and approved application i can use as so my clients can oauth login to the application and then in my interface i can manage their followers and followings?

[Chenin Boutwell]

If you have permission from the account owner to operate his account and he has given you the password, you can use it. If you are trying to "drive" someone else's account without permission, it would be illegal. If you have password and permission, there are many software available on internet through which you can handle your twitter account. Even you can handle more than one accounts via these software.