Have you been searching for alternatives to Asterisk? I do not know why in the world you want want to do that for!. How ever if you are looking for an alternative or Addon’’s that work with Asterisk?. Virtualhosting.com put together a list of the top 50 Opensource VoIP Applications out there. Its amazing how quickly VoIP is really picking up. I will post the first 7 on their list here and log to their blog so that you can read the rest.

SIP Proxies

SIP Proxies enable service providers to build scalable and reliable VoIP networks that are based on the Session Initiation Protocol. This allows a full array of call routing capabilities that make the most of network performance. Here are some of the most popular and successful SIP proxies on the market.

1. OpenSer: OpenSER has been described as a “mature and flexible” SIP server so it’s no surprise that it’s popular among users. OpenSER development began with FhG FOKUS SIP Express Router, but then diverged into its own feature-laden software package that was released in 2005. Since then it’s been exhibited around the world, and makes a great addition to Linux systems looking to employ VoIP technology.
2. VOCAL: Open source VoIP developers can benefit from the software and tools found in VOCAL. Developed through the Cisco sponsored labs at Vovida, VOCAL is fully customizable to business needs and can provide call routing, billing information, call control and more in an easy to control and maintain Linux based system. It’s been successful due largely in part to its immense capability for adaptation and scalability, and likely will only see further integration into business systems in the future.
3. partySIP: Developed back when VoIP was just starting to take off, partySIP can still be a relevant solution for businesses looking for VoIP today. This lies largely in the modular construction of partySIP, which relies on various plugins to add or remove capabilities. This flexibility allows its users to disable useless functions and enable new ones with very little development, making it easy to use and customize, which is likely the reason for users’ continued interest in the product.
4. SIP Express Router: This high performance SIP product can act as registrar, proxy or redirect server depending on your needs. It’s been widely successful in the VoIP market due to its ability to deal easily with operational problems like broken network components. Another reason it’s loved is its scalability from small office environments to acting as a PBX replacement and can in many cases act as a replacement for the very popular Asterisk system.
5. MjServer: One of the things that makes MjServer so important to the VoIP market is that it works on a variety of platforms, not just Linux, so those who aren’t quite ready to take the fully fledged open source route can ease into it. MjServer is a Java based application that is easily configurable and can act as a registrar, redirect or proxy in your VoIP setup, making it a versatile and useful tool for implementation.
6. OpenSBC: OpenSBC has been in use for over 7 years in both low and high volume applications. In this way, it’s a very reliable system, but also still employs a great deal of possibility for expansion and modification based on personal needs for the program. In fact, like most open source VoIP applications, the developers actively encourage the changing and development of the program to make it better for all users.
7. sipX: Developed by SIPFoundry, sipX is designed to be an incredibly feature rich and standards compliant infrastructure for businesses who want to employ VoIP technology. It is, in fact, one of the most widely used and well respected open source developments out there and feature wise is very similar to Asterisk.

Read more at their Blog here