Ever bought a piece of hardware and the software got EOLed? A Nokia phone perhaps? The Nokia Internet Tablets (Nokia 770, Nokia N800, Nokia N810, Nokia N810WME) are now legacy devices.

Because Maemo is open source there is a independent project based on Maemo, called Mer. This project aims to be more hardware agnostic (including support for mentioned Nokia Internet Tablets). It provides an up2date OS where Maemo is officially EOL by Nokia, but it is currently in heavy development therefore not production quality; it is aimed for developers and curious users.

So, where other Nokia products (S40 phones and S60 smartphones) become EOL and you're SOL you now have a choice to install a 3rd party firmware.