TrueOS (formerly PC-BSD or PCBSD) is a discontinued Unix-like, server-oriented operating system built upon the most recent releases of FreeBSD-CURRENT.

Up to 2018 it aimed to be easy to install by using a graphical installation program, and easy and ready-to-use immediately by providing KDE SC, Lumina, LXDE, MATE, or Xfce as the desktop environment. In June 2018 the developers announced that since TrueOS had become the core OS to provide a basis for other projects, the graphical installer had been removed. Graphical end-user-oriented OSes formerly based on TrueOS were GhostBSD and Trident. TrueOS provided official binary Nvidia and Intel drivers for hardware acceleration and an optional 3D desktop interface through KWin, and Wine is ready-to-use for running Microsoft Windows software. TrueOS was also able to run Linux software in addition to FreeBSD Ports collection and it had its own .txz package manager. TrueOS supported OpenZFS and the installer offered disk encryption with geli.

Development of TrueOS ended in 2020.

TrueOS was founded by FreeBSD professional Kris Moore in early 2005 as PC-BSD. In August 2006 it was voted the most beginner-friendly operating system by OSWeekly.com.

The first beta of the PC-BSD consisted of only a GUI installer to get the user up and running with a FreeBSD 6 system with KDE3 pre-configured. This was a major innovation for the time as anyone wishing to install FreeBSD would have to manually tweak and run through a text installer. Kris Moore's goal was to make FreeBSD easy for everyone to use on the desktop and has since diverged even more in the direction of usability by including additional GUI administration tools and .pbi application installers. PC-BSD's application installer management involved a different approach to installing software than many other Unix-like operating systems, up to and including version 8.2, by means of the pbiDIR website. Instead of using the FreeBSD Ports tree directly (although it remained available), PC-BSD used files with the .pbi filename extension (Push Button Installer) which, when double-clicked, brought up an installation wizard program. An autobuild system tracked the FreeBSD ports collection and generated new .pbi files daily. All software packages and dependencies were installed from inside of the .pbi files into their own self-contained directories in /Programs. This convention was aimed to decrease confusion about where binary programs reside, and to remove the possibility of a package breaking if system libraries are upgraded or changed, and to prevent dependency hell.

On October 10, 2006, PC-BSD was acquired by enterprise hardware provider iXsystems. iXsystems employed Kris Moore as a full-time developer and leader of the project. In November 2007, iXsystems entered into a distribution agreement with Fry's Electronics whereby Fry's Electronics stores nationwide carry boxed copies of PC-BSD version 1.4 (Da Vinci Edition). In January 2008, iXsystems entered into a similar agreement with Micro Center.

On September 1, 2016, the PC-BSD team announced that the name of the operating system would change to TrueOS. Along with the rebranding, the project also became a rolling release distribution, based on the FreeBSD-CURRENT branch.

On November 15, 2016, TrueOS began the transition from FreeBSD's rc.d to OpenRC as the default init system. Apart from Gentoo/Alt, where OpenRC was initially developed, this is the only other major BSD based operating system using OpenRC.