All sFlow agent implementations are subject to the sFlow license agreement,
https://sflow.org/developers/licensing.php. "sFlow is licensed free of charge from InMon Corporation. The purpose of the license is to ensure consistent and interoperable implementations, and correct use of the sFlow trademark and logo."
The open source Host sFlow agent,
https://sflow.net/, is widely used in open source network operating systems and you can find support on the mailing list.