The Luna Atra skill tool for Guild Wars 2 remains one of, if not the most popular, out of all those online. As a product, not only is regularly kept up to date but it's also incredibly slick and is probably one of the most attractive skill tools to use (can a skill tool be attractive?).
Despite all this, you cannot 'build' a character, you can only choose traits and skills. In contrast, Luna Atra's newly launched Guild Wars 2 Codex tries to address that in some minor ways, allowing users to share and rate builds, but still fails to really create an accurate numerical picture of what your character is when all items are considered.
Guild Wars 2 Build is the first fan made skill tool (as far as I'm aware) that allows you to not only pick your weapons and skills but also traits, sigils, amulet, jewel and runes. After you've done this, it then provides you with the exact attributes your character will have in structured PvP.
Firstly, it isn't quite perfect. Some traits that provide attribute bonuses don't yet factor and you can't choose varying runes (only a complete set). However, even in its infancy the tool shows great potential and I've already sunk countless hours into it theorycrafting.
The guys behind it deserve a lot of credit for what they've done, although I suspect it won't be long until Luna Atra jump on the band wagon and replicate their work.
So why not head on over and get lost in some theorycraft and show your support!
(p.s. that's my Engineer build; be gentle!)