If you have global traffic , Internet instability or outages on any particular region can affect your Application. Also With the faster adoption of online way of doing things Complexity is the new reality current web and mobile applications. And hence - If a third party internet outage or issue occurs, your brand is the one that is affected. Recently I was surprised to see so many site down alert Gomez network. I was looking form some online report which gives me a hint whether there is any ongoing internet outage from where the Gomez nodes reported us these problems. I had no choice but to use below some sites which gave me some stats about the internet instability on those areas:
On another note , the Submarine Cable Map is a free resource from TeleGeography which gives an active and planned submarine cable systems and their landing stations.
Hope this helps - and please don't forget to name some tools/sites that you have come across which helps the internet community worldwide or intends to notify about current ongoing outages or instability.
PS: Above is a snap from Akamai's Real-Time web monitor dashboard which is just intended to give a visual look on the topic for readers benifit. No copyright infringement intended, also neither I own these images nor I take credit for any of those images.