Can I use Appcrual without Freeagent?

Yes, you can. To sign up without FreeAgent integration you can go here: https://launchpad.appcrual.com/signup/

To sign up with FreeAgent integration, you can go here: https://launchpad.appcrual.com/signup_freeagent/

Regardless of the sign-up you follow you can always control your integration with FreeAgent in the Appcrual Settigns page.