This is a customized version of Asuswrt, the firmware developed and used by Asus on many of their routers.
Note: both "U" and "R" variants are supported (for example, RT-N66R).
The primary goals of this project are to fix bugs, add a few basic features and tweaks to the original firmware. This firmware will try to remain as close as possible to the original firmware. If you are looking for a slew of advanced features, then this project is not for you. Look at TomatoUSB or DD-WRT, two excellent products that might suit your needs better.
If however you prefer something as close as possible to the manufacturer's firmware, then this is for you
Latest stable release: 374.40 (374.40 alpha 4 for RT-AC68U) Latest beta release: 374.40 Beta 3 for RT-AC68U
Asuswrt-merlin provides the following changes over the original firmware:
Various bugfixes and optimizations
Some components were updated to newer versions, for improved stability and security
Persistent JFFS partition
User scripts that run on specific events
Ability to customize the config files used by the router services
LED control - put your Dark Knight in Stealth Mode by turning off all LEDs
Entware easy setup script (alternative to Optware - the two are mutually exclusive)
Optionally use shorter share names (folder name only)
Disk spindown after user-configurable inactivity timeout
NFS sharing (through webui)
Better compatibility with 3TB+ and Advanced Format HDDs