SlackBuildsOrg/network/xnetload

Xnetload displays a count and a graph of the traffic over a specified
network connection.

It either displays bytes/second or packets/second, based on the
capabilities of the kernel. On 2.1.x and later kernels (including the
2.2.x and 2.4.x series) it displays bytes/s. It requires the /proc
file system, or rather /proc/net/dev which is only found in Linux.
So AFAIK this program is Linux specific.