TrueOS has added the Wine-based PlayOnBSD package to their AppCafe library. With PlayOnBSD being available from TrueOS' AppCafe, it can be all GUI-driven now for getting Steam running on BSD. PlayOnBSD -- similar to PlayOnLinux -- automates much of the process for setting up Windows game/software under Wine.
Those interested in instructions can find details via TrueOS.org along with screenshots walking potential BSD gamers through the setup process. Of course, for gaming on BSD the NVIDIA binary driver is really the only option with the FreeBSD support for Radeon/Intel open-source graphics advancing but still not caught up to the mainline Linux driver state.