NOTE: You can find current, in-depth instructions for FreshTomato on Entware's wiki - Entware on FreshTomato (and other TomatoUSB forks)

Entware is a software package installer. It allows you to install programs that can't be included into FreshTomato itself, mainly due to most routers' limited flash RAM size. This example assumes you have a USB flash drive mounted under /mnt/sda1. If you need more details about configuring USB storage before reading this, see the USB Support page.

First, create the opt folder and mount it:

mkdir /mnt/sda1/opt
mount -o bind /mnt/sda1/opt /opt

Then, you can run the installation command:

/usr/sbin/entware-install.sh

Finally, you can install the packages you want, for example:

opkg update
opkg upgrade
opkg install htop