How to answer this question? Is it a valued resource on a per page basis or something else? Resources is so broad a category too. I feel in some cases that I would be providing an apples vs. oranges debate. Pathfinder and 3.5 have so many resources, some have to be useful. I have to say the 5E digital resources are largely rubbish so I do not think I will be heading there. Is there an indie game that I feel does it better?
I really love fleshing out new worlds and so most of my focus immediately leaps to products that help me do that. For the most part I use Realm Works which is a database system. Streamlined and intuitive I really love the way it organizes my material. But for it to be fully effective players need to be able to tap into that and they have to purchase software for that. I never make others buy stuff to be in my games so the product remains solely in use by me just as an organisational piece of software. That, plus it is RPG independent so not really a great answer for this.
Elthos – useful and a universal system
I reviewed a fledgling game a few years back called Elthos. It is a game system designed for a universal approach by the GM (i.e. any setting). It is also supported by an online system designed to assist all players in the understanding of the game. The person behind this system has been working hard over the past few years to update and refine this online tool into a really useful piece of kit. The online support (called the Mythos Machine) is in open beta at the moment too so it is a great time to check out how it all works.
I love a good Universal System and Elthos works solidly. It does have a bent toward Fantasy RPG language but you can use it in any imaginable way. Do yourself a favor and have a look at the system and sign on to the beta. The more people using it the better it will be and in a word, that is useful. Keep rolling!