Key free SIP components maintained by iptel.org include:

• SER [1] -- SIP Express Router, RFC3261 SIP proxy
• SEMS [2] -- SIP Express Media Server
• SERweb [3] -- web interface to SERi [4]
• RTP Proxy [5] -- media relay for NATi [6] traversal (courtesy of Maxim Sobolev)
  
• SER command-line tools [7]: seri [8]_* (ser_ctl, ser_cred, ser_rpc, ser_user, ser_attr, ser_domain, ser_uri)
• mystun [9] -- STUN server
  

Besides that, many third-party free tools have been reported to be used along with iptel.org SIP software.

• Accounting
• • CDR Tool [10] tool for CDRi [11] postprocessing
  • OSP Toolkit [12]
    
• Command-line tools
  
• • pua [13] -- command line presence UA
  • SER command-line tools [14]: ser_* (ser_ctl, ser_cred, ser_rpc, ser_user, ser_attr, ser_domain, ser_uri)
• Embedded
• • milkfish [15] -- home router
• NATs
• • SIP connection tracking [16]
  • restund [17] -- STUN/TURN server
• PSTNi [18]
• • Asterisk [19] -- popular open source PSTN gateway
    
• Security
• • sipcrack [20] tool for dictionary attacks
  • sipbot [21]
    
  • smap [22] port scanner
  • protos [23] buffer overflow testing tool
  • Tactical VoIP toolkit [24] - VoIPi [25] security assessment tool
  • see also Mohamen Nassar's list of further security tools [26], and VOIPSA's security tool list [27].
    
• Stacks
• • libre [28] -- SIP, SDPi [29], RTPi [30]/RTCPi [31], STUN/TURN/ICE, BFCP and DNS
  • sofia-sip [32]
  • pjsip [33]
    
• Testing
• • sipp [34] performance stress tool
  • seagull [35] -- IMSi [36] traffic generator
    
• Troubleshooting
• • ethereal [37] tool for capturing VoIP (and other) traffic and analyzing it
  • routegraph [38] -- creates call graphs for SER configuration files
    
  • SIP Analyzer [39]
  • SIP v6 analyzer [40]
  • sipgrep [41] -- filtering of SIP messages
    
  • sipsak [42] traceroute-like tool for SIP (with many other features); also easy to integrate into monitoring applications such as argus [43], nagios [44]
  • sipscenario [45] tool for generating HTML-ized traces of SIP messages
  • sipspy [46] -- tool for capturing and graphical representation of SIP traffic in multiple nodes
    
  • wist [47] -- remote SIP tracing
  • see also Klaus Darilion's list of SIP testing tools [48]
    
• UA
• • baresip [49] -- command line high quality voice + video softphone
  • jitsi [50] -- (formerly SIP-Communicator) cross platform voice + IM + video Java client
  • kphone [51]
  • minisip [52] -- SIP UA
  • Twinkle [53]