Cisco
(from Cisco FAQ) Routers running GSYS version 9.21(4) and 10.0(3) as well as later releases.
Wellfleet/Bay
(from Wellfleet FAQ) DHCP is supported by enabling BOOTP support (with transmission and/or reception as needed). Starting with version 9.00 of their routing software BayRs.
3Com Netbuilder
Version 7.2 software can support DHCP relaying through the use of its generic UDP Helper service. Version 8.0 and later officially supports DHCP.
Xyplex
Version 5.5 of their routing software supports DHCP.
ALANTEC
The switches’ “router” function has have been handling BOOTP forwarding since around 1993. Support for the broadcast flag introduced in a maintenance release of 2.5 of their software and is in version 2.6 and later.
IBM 2210
I’ve confirmed that Version 1 Release 2 has a BOOTP relay agent. I haven’t found out anything about support for the broadcast flag.
ACC
Version 7.2 (about 1994) and later support DHCP relaying.
Proteon/Digital
I’m not sure what is the first version that has this support.
Novell MPR
The same as for their server.
IBM 6611
Supports BOOTP forwarding.