Good free alternative to Gmail Boomerang?

Hello everyone. I'm not sure this is the right topic to answer this question, but I'll give it a shot.
I'm looking for good Gmail extension like Boomerang to schedule emails and make reminders, preferably for free. I need to schedule a lot of work related emails, but can't afford Boomerang because there are other more important things I need to pay for. Thank you in advance.