Chrome: Ever receive a bunch of emails that all require the same reply, but aren't part of the same thread? Batch Reply for Gmail is a simple extension that lets you select a few different conversations, and reply back to all of them with one email.
Batch Reply for Gmail adds a button to Gmail so you can quickly select conversations, and then reply to all of them at once. Check the boxes of the emails you want to reply to, and click the big Reply button up top. It's not very different from sending out a brand new email with different recipients, but it's a little quicker. It could come in handy for those days when you get a bunch of happy birthday emails or when you want to get a few people involved in a thread quickly.