because of licensing concerns, the openbsd team has reimplemented software from scratch or adopted suitable existing software. for example, openbsd developers created the pf packet filter after unacceptable restrictions were imposed on ipfilter. pf first appeared in openbsd 3.0 and is now available in many other operating systems. openbsd developers have also replaced gpl-licensed tools (such as cvs, diff, grep and pkg-config) with permissively licensed equivalents.