Pentadactyl was forked from Vimperator, mainly because of internal differences between the developers. Both projects have currently two active developers and a few people supporting them with patches.

After the fork, however, the projects have rethought their mission, and have so far diverged significantly. Without going into details about feature differences (both have some unique features), the main difference is more about internal design decisions:

Vimperator

Vimperator 3 and onwards are mainly influenced by projects like Firefox4 or Gnome3. The main ideas we took from both are:

• Focus on usability: It's much easier to just add 10 new features or options than really think about the problem statement. Vimperator takes the second approach. It thinks about what the (power) user wants to actually achieve and tries to create an interface which Just Works (tm).

• Focus on simplicity: Any obscure feature which maybe 2 people in the world want can make the whole software more complex for hundred thousands of other users. It also adds much complexity inside the program code, which leads to bugs.

• Focus on stability: While we might have less features, the final aim is to have those which we have as bug free and complete as possible. I know, that we aren't here yet, but for Vimperator 4+ that really will be a high priority.

• Focus on design: Hey, we live in the 2010s - not the 1990s anymore. Software CAN be nice to look at. We do have the graphical abilities, and when done right, it neither wastes too much space nor resources nor time. You can also achieve affects with graphical abilities which can't be done with a text-only interface. Just try Gnome3: The interface just "feels" so organic, you don't even think about it, it just works.

In general, the main Vimperator developer reads lots of blogs from real usability experts like Aza Raskin (was the main UI designer for Firefox) or others. Noteable posts include:

• http://www.azarask.in/blog/post/the-wrong-problem/
• http://m.omgubuntu.co.uk/2011/03/unity/?wpmp_switcher=mobile

Pentadactyl

Pentadactyl on the other hand is more commited to being vim-like (while still not 100%) and a tool which is best used by programmers.

• More dedication to 100% Vim compatibility: While the key bindings are nearly the same as Vimperator, commands and options and visual design follow Vim much more closely than Vimperator.

• Massive customizability: There is an option for every (un-)imaginable thing and many commands for things you probably never need so that it's hard to find the ones which you need.

• Constant changes: There are certainly more commits on a daily basis than in Vimperator, but many (most?) of them just fix things which got broken before. So if you like a lively development with daily bug fixes and introduction of new bugs, Pentadactyl is for you.

Summary

Anyway, if you really want a 1:1 vim clone, then Pentadactyl is probably the better option for you. If you want a vim-inspired, but modern interpretation of a modal browser with high focus on usability, then you'll love Vimperator 3.x and future versions.