Trillian Alternatives for Windows

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.

Tox is a free, open-source, and secure peer-to-peer instant messaging and video calling protocol designed for strong privacy and censorship resistance. It provides end-to-end encrypted communications without reliance on central servers.

Signal is a secure, open-source messaging application that uses end-to-end encryption to protect user communications. It offers text messaging, voice and video calls, group chats, and file sharing, all with a strong focus on privacy and security. Available on multiple platforms, Signal is a leading choice for individuals prioritizing confidential conversations.

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.

Digsby was a multi-protocol instant messaging client that unified connections to various chat networks and social media platforms. It allowed users to manage their conversations and updates from services like Aim, Msn, Yahoo, Twitter, Facebook, and Myspace all within a single, integrated application.

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.

Glip, by RingCentral, is a comprehensive team collaboration platform combining real-time messaging, video calls, task management, and file sharing into a single, searchable hub. Designed to streamline communication and workflow, it aims to replace disjointed tools with a unified digital workspace.

ICQ is a veteran instant messaging platform offering a wide range of communication features, including text chat, voice and video calls, screen sharing, and group chats. It aims to provide a reliable and feature-rich messaging experience with a focus on privacy and security.

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.

Miranda NG is a highly extensible, multi-protocol instant messaging client for Windows. A successor to the popular Miranda IM, it offers a modular architecture supporting numerous chat networks, allowing users to consolidate their conversations into a single interface. It's designed for resource efficiency and deep customization.

Quassel IRC is a powerful, distributed, and cross-platform IRC client designed for continuous connectivity and efficient management of multiple IRC networks and conversations.

Instantbird is a powerful, cross-platform instant messaging client built on Mozilla's XULRunner, leveraging the robust libpurple library from Pidgin. It supports a wide array of instant messaging protocols, offering a unified chat experience.

Spark is a free, open-source instant messaging client optimized for businesses and organizations. It integrates seamlessly with Openfire servers and supports a wide range of features including group chat, file transfers, and screen sharing, making it a versatile communication tool.

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.

Psi+ is a robust, cross-platform XMPP/Jabber client tailored for users who prioritize control, privacy, and extensibility. As a development branch of the classic Psi client, it offers advanced features for secure and customizable instant messaging.

Rambox is a FOSS and portable messaging and emailing application that consolidates numerous web services into a single, convenient interface. It supports a wide array of communication and collaboration platforms, including popular chat, email, and social media services, offering a unified experience with features like unified inbox and notifications.

Tencent QQ (QQ) is a versatile instant messaging and social platform widely used in China and expandingglobally. It offers a wide range of communication tools including text chat, voice and video calls, group chats, and file sharing.

Bit Chat is a secure, open-source, peer-to-peer instant messenger platform that prioritizes user privacy and security through robust end-to-end encryption and a decentralized network architecture. It empowers users with direct, encrypted communication, bypassing central servers and enhancing resistance to surveillance and censorship.

Zulip is a powerful open-source group chat application designed for team collaboration. It uniquely structures conversations around topics, enabling users to easily catch up on important discussions and manage information overload. Zulip facilitates secure communication with integrated file sharing and various integrations.

Coccinella is a free and open-source, cross-platform XMPP/Jabber client. It offers secure instant messaging, group chat, voice chat, and a unique interactive whiteboard feature. Designed with privacy and security in mind, Coccinella provides encrypted communications and supports various communication protocols for a flexible messaging experience on Windows, macOS, and Linux.

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.