First, please understand that this is highly experimental. The app is not even in the Pebble App Store.
iMsgQuickReply is a Pebble app that will allow you to send quick replies to your iMessage contacts. It needs an iMessage bridge. So, you will need an OS X computer, preferably running as a server.
As you know, iOS APIs don’t allow you to send specific actions to a notification you’ve just received. It is a known limitation of ACNS. Using this hack, you will be able to reproduce a quick reply behavior with your Pebble.
You won’t be able to send a quick reply to a notification you just received. This app will just allow you to send quick replies to a list of contacts you previously specified.