UWSim requires a PC running GNU/Linux and with a decent graphics card (i.e. NVidia or ATI). It is being mainly developed using Ubuntu. MacOS and Windows are not supported at this moment, although it should be possible to run UWSim on them, since all the dependencies are also available for these systems.
UWSim depends on OpenSceneGraph and osgOcean, which are both available as open source. Additionally, if physics simulation is required, further dependencies include Bullet, osgWorks and osgBullet, open source projects as well.
Please find the download and installation instructions in the corresponding wiki page.