Open OSCAR Server is an open-source instant messaging server written in golang, compatible with classic AIM and ICQ clients. The project is independently developed and not affiliated with AOL or Yahoo! Inc. It supports a range of legacy clients including AIM versions 1.x through 7.x, TOC1 and TOC2 protocol clients, and various ICQ versions from 98x to 5. Features include instant messaging, buddy lists, chat rooms, public and private chat exchanges, user profiles, privacy controls, presence statuses, offline messaging, and file sharing over LAN and direct connect.

The server offers quickstart guides for Linux (x86_64), macOS (Intel and Apple Silicon), and Windows 10/11 (x86_64). Users without AIM or ICQ installed can follow dedicated client setup guides. The project is under active development and welcomes contributions. A Discord server is available for community support and involvement.

Administrative tasks can be managed via a Management API with endpoints for listing, creating, and deleting users, changing passwords, listing active sessions, and creating or listing public chat rooms. Commands are provided for both PowerShell (Windows) and curl (macOS/Linux/FreeBSD).

Open OSCAR Server is licensed under the MIT license, making it freely available for self-hosting and modification.