I'm not sure if I get your question right.
Lazy Approval is designed for replying to tasks by email. And you are asking for an alternative to be able to approve though an email.
What would the alternative need to bring in so you would pick it instead of Lazy Approval?
An alternative (not mail-based though) could be Nintex Mobile, where users get a push notification for new tasks and respond to them in the mobile app.
Would that be an alternative?