It's running Windows CE 3.0, and that's a good thing. This might be an ancient OS, but this tablet is still more capable as an ereader than almost any Android tablet. Actually the fact the Viewpad 100 is running a version of Windows is a plus, no matter how old it is. It behaves like Windows so I didn't have to relearn anything.
Some time back I did a survey of PDF apps for Android. None of the free ones were very good, not even Adobe's.But with the Viewpad 100 I can use Adobe Reader v2.0, which has more features than does Adobe Reader 9 on Android. I can basically do everything that Adobe Reader does on a PC on my Viewpad 100.
As for ebooks, I've started using an old version of Mobipocket Reader (think of it as the granddaddy of the Kindle apps). This app falls short against Aldiko, but ti's better than any of the other free reading apps. In fact, it can do one thing that is an absolute necessity on large screens: it can show the text in 2 columns. I love that.
Click on the picture at right to see an example. I can add other formats like MSReader and eReader, but for me PDF and Mobipocket are the 2 I need most.
And then there's the other software (which is far more than I can cover here). The Viewpad 100 ships with Pocket Office, which means I have a what's pretty close to clone of Word 98. If I plug in a keyboard I can type out a full paper and save it in any number of formats. You can't do that with Android. Format support is limited, and keyboard support is incomplete. If I wanted, I could also buy a copy of Softmaker, and then I'd have the equivalent of MS Word 2010 with all the features and format support. Note that most Android office apps don't have the format support you'd expect from MS Word.
There are a number of other reasons I like the Viewpad 100, but the main point I want to make with this post is to say that old doesn't mean useless. Also, Android isn't as great as some claim; the apps don't amount to much when compared to older OSes.