postActiv is described as 'free and open source social networking project based on GNU Social. It uses OStatus, which means that users can for example connect to users on Mastodon and GNU Social instances as well' and is an app in the Social & Communications category. There are eight alternatives to postActiv for a variety of platforms, including Self-Hosted solutions, Online / Web-based, iPhone, Blackberry and Android Tablet. The best alternative is Mastodon, which is both free and Open Source. Other great apps like postActiv are Friendica (Free, Open Source), Pleroma (Free, Open Source), GNU social (Free, Open Source) and VK (Free).
Mastodon is a decentralized microblogging engine. FEATURES - Free and open-source. - Decentralized, no worries about a single company controlling your communications. - Supports the standardized ActivityPub protocol - Fully interoperable with...
Friendica is a distributed social network application. Which allow users to connect with others via their own Friendica server, but may also fully integrate contacts from other platforms including Twitter, diaspora*, Pump.io and StatusNet into their 'newsfeed'.
VK (originally VKontakte) is a largest social network service from Europe. Available in many languages and highly popular particularly among Russian-speaking users around the world, especially in Russia, Ukraine, Kazakhstan, Moldova, Belarus, and Israel.