Jetable is described as 'To avoid spam, jetable.org provides you with a temporary email address'. There are more than 50 alternatives to Jetable, not only websites but also apps for a variety of platforms, including Windows, Firefox, Linux and Android. The best alternative is MailDrop, which is both free and Open Source. Other great sites and apps similar to Jetable are Spamgourmet (Free, Open Source), 10 Minute Mail (Free), Burner Mail (Freemium) and Mailinator (Freemium).
MailDrop is a free throwaway e-mail address. It's temporary. It's transient. It's disposable. It's meant for those times when you don't want to give out your real address. Just give someone any e-mail address in the maildrop.
Spamgourmet provides disposable, optionally self destructing, email addresses that get created automatically the first time they are used, forward messages, and then automatically expire after number of specified messages received.
Guerrilla Mail gives you a disposable email address. You can give your email address to whomever you don't trust. You can read the email using Guerrilla Mail, click on any confirmation link, and even reply.
Bouncr allows you to hide your permanent email address behind an '@boun.cr' address. You then share it however and with whomever you wish. Anytime you're receiving unwanted emails, simply cancel your Bouncr address and it's gone.