SmartOS is a free and open-source SVR4 hypervisor based on the UNIX operating system that combines OpenSolaris technology with Linux's KVM virtualization. Its core kernel contributed to the illumos project. It features several technologies: Crossbow, DTrace, KVM, ZFS, and Zones.  Unlike other illumos distributions, SmartOS employs NetBSD pkgsrc package management. SmartOS is designed to be particularly suitable for building clouds and generating appliances. It was originally developed for and by Joyent, who announced in April 2022 that they had sold their business supporting and developing it to MNX Solutions.[8] It is open-source and free for anyone to use.

SmartOS is an in-memory operating system and boots directly into random-access memory. It supports various boot mechanisms such as booting from hard drive, USB thumbdrive, ISO Image, or over the network via PXE boot. One of the many benefits of employing this boot mechanism is that operating system upgrades are trivial, simply requiring a reboot from a newer SmartOS image version.

SmartOS follows a strict local node storage architecture. This means that virtual machines are stored locally on each node and do not boot over the network from a central SAN or NAS. This helps ensure that network latency issues are eliminated as well as to preserve node independence. Multi-node SmartOS clouds can be managed via the open-source[10] Joyent Triton DataCenter (formerly known as SmartDataCenter cloud orchestration suite or via the Project Fifo  Open Source SmartOS Cloud management platform built on Erlang.