Syllable Desktop is a discontinued free and open-source operating system for Pentium and compatible processors. Its purpose is to create an easy-to-use desktop operating system for the home and small office user. It was forked from the stagnant AtheOS in July 2002.

It has a native web browser (Webster, which is WebKit-based), email client (Whisper), media player, IDE, and many more applications.

Another version of Syllable OS is the Syllable Server, which is based on Linux core.

Features according to the official website include:

• Native 64-bit journaled file system, the AtheOS File System (usually abbreviated to AFS in this context; not to be confused with the Andrew File System which shares the same abbreviation)
• C++ oriented API
• Object-oriented graphical desktop environment on a native GUI architecture
• Mostly POSIX compliant
• Software ports, including Vim, Perl, Python, Apache, others.
• GNU toolchain (GCC, Glibc, Binutils, Make)
• Preemptive multitasking with multithreading
• Symmetric multiprocessing (multiple processor) support
• Device drivers for most common hardware (video, sound, network chips)
• File system drivers for FAT (read/write), NTFS (read) and ext2 (read)
• Rebol as system scripting language

• Haiku (operating system)