Top Alternatives to Spark

Pidgin is a free and open-source multi-protocol instant messaging client designed to connect users across various chat networks with a single application. It's highly extensible through plugins and supports a wide range of protocols including XMPP, ICQ, and IRC.

Adium is a free and open-source instant messaging client for macOS, designed to connect to multiple chat networks simultaneously. Supporting protocols like Jabber (XMPP), Google Talk, AOL Instant Messenger (AIM), ICQ, MSN Messenger, and Yahoo! Messenger, Adium provides a unified interface for all your conversations.

Trillian is a versatile, multi-protocol instant messaging client that unifies various communication platforms like IRC, XMPP, and more into a single, user-friendly interface. It's designed for both personal and team collaboration, offering features like encrypted chats, group collaboration tools, and extensive customization options.

Jitsi is a free and open-source suite of secure, flexible communication tools. It offers multi-platform support for voice (VoIP), video conferencing, and instant messaging, emphasizing privacy and ease of use with no account required to start a meeting.

Miranda IM is a lightweight, open-source, multi-protocol instant messaging client designed specifically for Microsoft Windows. Known for its extensibility and resource efficiency, it allows users to connect to various chat networks simultaneously through a flexible plugin-based architecture.

Empathy is a versatile multi-protocol messaging client designed for text, voice, and video communication across numerous IM networks. It offers features like file transfers, location sharing, and integration with various services, providing a unified communication experience.

IM+ is a versatile instant messaging application designed to unify communication across multiple platforms. It supports a wide array of popular services, including Google Talk, Twitter DMs, Yahoo!, AIM/iChat, ICQ, Jabber, and even Slack. IM+ simplifies staying connected with friends, family, and colleagues, offering a centralized hub for all your chat needs.

Psi is a robust, open-source instant messaging client built on the XMPP protocol. It's known for its focus on speed, efficiency, and adherence to XMPP standards, offering a clean interface and strong privacy features for secure and reliable communication.

Gajim is a free and open-source instant messaging client for the XMPP protocol. Built using the GTK+ toolkit, it offers a wide array of features for secure and flexible communication, including encrypted chat, group conversations, multi-protocol support via gateways, and extensive customization options.

qutIM is a free and open-source, multi-protocol instant messenger designed for connecting to various networks including ICQ, Jabber, Mail.Ru, IRC, and VKontakte. It offers a unified interface for managing multiple accounts and conversations.

KakaoTalk is a popular mobile messaging service offering free text, voice, and video calls. Primarily used in South Korea, it provides a comprehensive communication platform with features like group chats, stickers, and a strong emphasis on user privacy and security.

Disa is a unified messaging hub that consolidates conversations from various services like SMS, Facebook, and WhatsApp into a single interface, simplifying communication management.

Tkabber is a free and open-source instant messaging client specifically designed for the XMPP protocol. Built with the Tk toolkit, it offers a lightweight yet extensible platform for text-based chat, group conversations, and various interactive functionalities supported by XMPP.

YakYak is an unofficial desktop client for Google Hangouts, providing a dedicated application experience outside of a web browser with features focused on convenience and improved usability.