net-acct was developed by Ulrich Callmeier. The Mekafile hints that it can be used on Solaris (using libpcap). The Linux version uses the now obsolete packet interface at protocol level. (see ip(7)).
I had tried to implement support for the newer packet interface at device level (supported since Linux kernel versions 2.2, see packet(7)), but I found that it lost packets in high load situations. Patches against net-acctd are available on request.
ulog-acctd is based on net-acct and still shares some portions of the
code.