I worked with someone on a Lisp project that monitors the bitcoin blockchain for new transactions, coins sent and confirmations. It could be converted into a type of address monitoring service for multiple blockchains - just needs work, but it's a solid piece of software.

I paid and worked on its development a few months ago, and have since stopped paying for hosting. But it's all there ready to go. I wasn't into altcoins at that point, but I can see a future in it now. It was called donebit.