1. GPL Perl Code
2. Well-written with Modular Design
3. Templating
4. Easy attachments (uploads)

At the time, I stumbled across TWiki but interpreted the registration to get source code to be a bad indicator and moved on, eventually writing my own wiki.

At some point, I realised that TWiki was a superset of my own wiki, and was more featureful, so I took the plunge, registered to download the sources, and installed my own TWiki wiki.

It has taken some time and quite a bit of work to tweak the HTML templates in TWiki to what I consider an acceptably simple layout, but it's done. TWiki's biggest weakness is in the default templates provided, which should have these features:

1. Simple layout
2. Demonstrates maximum number of templating features
3. Allows simplest re-write to webmaster's preferences

I believe TWiki's default templates accomplish none of these goals (although it comes close to goal #2). In any case, TWiki code itself is well-written and I NEVER recommend someone download/install my wiki (or usemod wiki) rather than TWiki. TWiki simply has every feature that you could want, and then some.