These versions are designed for embedding on web sites. To keep them as small as possible, they lack most of the symbols found in the Print/PDF version and have no Greek Extended, Small Capitals, or Alternative Fractions, but they do have Petite Capitals.

They contain OpenType features, such as Petite Capitals, Capitals to Petite Capitals, Standard Ligatures, Discretionary Ligatures, Superscripts, Subscripts, Scientific Inferiors, Ordinals, OldStyle Figures,  Stylstic Sets, Character Variants, Fractions, and Kerning.

They have fontnames as the Print/PDF versions, so it is not possible to install them simultaneously, but the filenames are different to avoid overwriting one version with the other. Make sure that you have the appropriate version installed for Print or Web publishing. 

The WOFF (Web Open Font Format) versions are the same as the OpenType Web versions, but compressed. The disadvantage is that they cannot be installed in Windows and cannot be embedded automatically using Serif WebPlus X8.  You will need to add suitable @FontFace code manually to make use of them.