Top Alternatives to Spark

Pidgin is a free and open-source chat client which supports AIM, Google Talk, ICQ, XMPP protocols.

Adium is an Open source multi-protocol instant messaging client for Mac OS X, supports MSN, Jabber, Yahoo! and other networks.

Trillian is a proprietary multiprotocol instant messaging application.

Jitsi (formerly SIP Communicator) is a free and open source multiplatform voice (VoIP), videoconferencing and instant messaging application.

Miranda IM is an open source multiprotocol instant messaging application, designed for Microsoft Windows.

Empathy is an instant messaging (IM) and voice over IP (VoIP) client which supports text, voice, video, file transfers, and inter-application communication over various IM protocols.

IM+ supports simultaneously major IM services, including Google Talk, Twitter DMs, Yahoo!, AIM/iChat, ICQ, Jabber (and Slack through Jabber), etc.

Psi is a free instant messaging application designed for the XMPP network (including Google Talk). Fast and lightweight, Psi is fully open-source and compatible with Windows, Linux, and Mac OS X.

Gajim is an instant messaging client for the XMPP protocol which uses the GTK+ toolkit.

qutIM is free and open-source multiprotocol (ICQ, Jabber, Mail.Ru, IRC, VKontakte) instant messenger.

KakaoTalk (Korean: 카카오톡), or sometimes KaTalk, is a free mobile instant messaging application for smartphones with free text and free call features.

Disa is your new messaging hub. Conversations from different services can seamlessly be joined together, or disbanded within seconds.

Tkabber is a GPL instant messaging client for the XMPP protocol which uses the Tk toolkit for the GUI.

YakYak is a desktop chat client for Google Hangouts.