They usually contain both vector and bitmap components, but are only usually used in illustrations and content created in drawing or presentation applications. For example, most clipart in Windows is in the WMF format. Normally there's no way of working with them on Macs unless you have a special application, such as WMF Viewer.
WMF Viewer allows you to view WMF files on Mac and also convert them to vector and raster formats, including PDF(vector), EPS, JPG, GIF, TIF, PSD, PICT, PNG, BMP, SGI. There's not a great deal you can do with them beyond that though, other than navigate through a series of images using the arrow keys, or rotate them using the handy rotation dial. All the conversion file formats are listed in the drop-down menu in the bottom-right, and you can convert either one image at a time or a batch of images, using the 'Convert' or 'Convert All' buttons at the top. You can also change the resolution exported to although this is limited to 4 presets - 72, 150, 300 and 600 dpi.
There's nothing fancy about WMF Viewer, but if you have to work with Windows WMF files its a quick way to view or convert them.
- functionality improved interface changes made
WMF Viewer supports the following formats
WMF, PDF (vector), EPS, JPG, GIF, TIF, PSD, PICT, PNG, BMP, SGI.