Android: Interpreting the flashes emitted by your Android smartphone's LED can be difficult, especially when they're all the same colour. Light Flow lets you adjust the colours and patterns for individual apps.
Light Flow has been around for a while, but we've actually never covered it before. It lets you customise the colour, duration and rate of LED notifications for different apps. If you receive multiple notifications (such as an email, an SMS, and notifications from Facebook and Twitter), it will cycle through the colour for each, so you're aware of all four notifications -- not just the latest one. There's a free version of the app available, but if you don't mind parting with $2.49, the paid version cycles through colours faster -- every 2.5 seconds rather than every 20.
It's not guaranteed to work with every phone on the market, but it's definitely worth taking the free version for a test drive to see if it works for you. It seems to have a better handset compatibility rate than previously mentionedLEDBlinker, and the number of supported apps is seriously impressive -- over 600 in the full version.