Originally Posted by DrageMester

.pps files can be opened with Microsoft PowerPoint (part of Microsoft Office) or with Microsoft PowerPoint Viewer (freeware).

But be careful of opening strange files that are sent to you - if it's from an unknown source, don't open it. If it's from someone you know, check first that they actually sent it to you (and that it isn't someone else faking their address or a virus/work that infected their computer).