Features

lldpd supports several discovery protocols and is smart enough to select the right protocol on each interface:

LLDP, of course
CDP (Cisco)
EDP (Extreme)
SONMP (Nortel)
FDP (Foundry)

It is able to advertise the following TLV:

System name and description
Port name and description
VLAN ID and names
IPv4/IPv6 management address
MAC/PHY information
MDI power (802.3af and 802.3at)
Link aggregation
Network policies (LLDP-MED)
Location (LLDP-MED)
Inventory (LLDP-MED)

lldpd supports many OS:

GNU/Linux
FreeBSD
NetBSD
OpenBSD
macOS
Solaris

Moreover, it can handle correctly VLAN, link aggregates and bridges on all those platforms, except on Solaris.

Discovered neighbors can be queried through a convenient command line interface:

# show neighbors detail
-------------------------------------------------------------------------------
Interface:    eth0, via: LLDP, RID: 1, Time: 0 day, 00:00:10
  Chassis:     
    ChassisID:    mac 00:18:f3:03:4e:06
    SysName:      dev-01.example.com
    SysDescr:     Debian GNU/Linux 7.0 (wheezy) Linux 3.7-trunk-amd64 #1 SMP Debian 3.7.1-1~experimental.1 x86_64
    MgmtIP:       192.168.20.127
    Capability:   Bridge, on
    Capability:   Router, on
    Capability:   Wlan, off
  Port:        
    PortID:       mac ea:b8:ab:aa:8c:da
    PortDescr:    eth1
    PMD autoneg:  supported: no, enabled: no
      MAU oper type: 10GigBaseR - R PCS/PMA, unknown PMD.
  LLDP-MED:    
    Device Type:  Media Endpoint (Class II)
    Capability:   Capabilities
    Capability:   Policy
    Capability:   Location
    Capability:   MDI/PSE
    Capability:   MDI/PD
    Capability:   Inventory
    Inventory:   
      Hardware Revision: System Version
      Software Revision: 3.7-trunk-amd64
      Firmware Revision: 2104   
      Serial Number: System Serial Number
      Manufacturer: System manufacturer
      Model:        System Product Name
      Asset ID:     Asset-1234567890
-------------------------------------------------------------------------------

They can also be queried through SNMP with the built-in SNMP subagent. Or through a Unix socket with the provided library.