MyNotify for Android
The list of apps being monitored is configurable; defaulting to GMail, Messaging, Phone and GTalk.
Notifications occur at a set interval for a duration of time; can be on a schedule; can be stopped if the device battery is too low or the device is in a bag.
New: Pebble smartwatch notification support is included, so you can turn off all other notifications and just use a Pebble.
N.B. You will see a warning from the Accessibility system.
This warning is generic, as it cannot tell what a service monitors, but MyNotify only monitors Notifications.
by U####:
Great app but keeps force closing and then goes back to original notification settings. Needs a save feature after setting which apps should receive notifications.