It depends on the kind of service your webapp is offering. If it's possible to use your app to create/enter data and then save it later, let your users do it.

It depends on the kind of service your webapp is offering. If it's possible to use your app to create/enter data and then save it later, let your users do it. If the user is logged in, save it if not ask them to sign in and save it or signup. This would give your first-time visitors a demo of your app too. Sign in or Log in. I too hadn't thought about this before. Had used 'login' previously till today. But I think I'll choose to use 'Sign in' from today. But IMO when using 'Sign in' it's better to use 'Register' instead of 'Signup'. Both words sound totally different and don't cause confusion. Whereas 'login' would go hand in hand with 'Signup' or I guess it's upto you.