Software

Easy to use but advanced IP PBX system, VoIP gateway and conference server. ([Source Code](https://github.com/asterisk/asterisk))

Complete, modular and scalable SIP server, includes a push gateway, to deliver SIP incoming calls or text messages on mobile device platforms where push notifications are required to receive information when the app is not active in the foreground. ([Source Code](https://github.com/BelledonneCommunications/flexisip))

Web-based open source GUI that controls and manages Asterisk. ([Source Code](https://git.freepbx.org/projects/FREEPBX))

Scalable open source cross-platform telephony platform. ([Source Code](https://github.com/signalwire/freeswitch))

Web interface for multi-platform voice switch called FreeSWITCH. ([Source Code](https://github.com/fusionpbx/fusionpbx))

Modular SIP server (registrar/proxy/router/etc). ([Source Code](https://github.com/kamailio/kamailio))

SIP proxy/server for voice, video, IM, presence and any other SIP extensions. ([Source Code](https://github.com/OpenSIPS/opensips))

Lightweight SIP proxy, location server, and registrar for a reliable and scalable SIP infrastructure. ([Source Code](https://github.com/fonoster/routr))

VoIP troubleshooting and monitoring platform. ([Demo](https://demo.sip3.io), [Source Code](https://github.com/sip3io/))

Troubleshooting and monitoring VoIP calls. ([Source Code](https://github.com/sipcapture/homer))

Full-featured IPBX solution built atop Asterisk with integrated Web administration interface and REST-ful API. ([Source Code](https://github.com/wazo-platform))

Transit class4 softswitch(SBC) with integrated billing and routing engine and REST API. ([Demo](https://demo.yeti-switch.org/), [Source Code](https://github.com/yeti-switch))

Federated microblogging server with Mastodon, GNU social, and ActivityPub compatibility. ([Source Code](https://akkoma.dev/AkkomaGang/akkoma))

Knowledge-based community software. You can use it to quickly build your Q&A community for product technical support, customer support, user communication, and more. ([Source Code](https://github.com/apache/answer))

Comment system built in Golang, providing a lightweight and highly customizable solution for adding comments to your website. ([Source Code](https://github.com/ArtalkJS/Artalk))

Fast, SQLite-powered forum engine written in ASM. ([Source Code](https://asm32.info/fossil/asmbb/index))

Powerful plugin that takes your WordPress.org powered site beyond the blog with social-network features like user profiles, activity streams, user groups, and more. ([Source Code](https://github.com/buddypress/BuddyPress))

Privacy-friendly and customizable Disqus (comment system) alternate. ([Demo](https://chirpy.dev/play), [Source Code](https://github.com/devrsi0n/chirpy))

A better commenting experience from Vox Media. ([Source Code](https://github.com/coralproject/talk))

Distributed social networking server. ([Source Code](https://github.com/diaspora/diaspora))

Advanced forum / community solution based on Ruby and JS. ([Demo](https://try.discourse.org/), [Source Code](https://github.com/discourse/discourse))

Powerful open source social networking engine. ([Source Code](https://github.com/Elgg/Elgg))

Enigma 1/2 is a modern, multi-platform BBS engine with unlimited "callers" and legacy DOS door game support. ([Source Code](https://github.com/NuSkooler/enigma-bbs))

Delightfully simple forums. Flarum is the next-generation forum software that makes online discussion fun again. ([Source Code](https://github.com/flarum/flarum))