Steem.center is pretty much best summed up as a "Wiki" of Steem.
It covers just about everything and as time goes on it is being updated regularly.
This is definitely one of the best overall if not the best overall tool/source for information about Steem.
Thanks to: @someguy123 (Witness)
By far one of the most used resources that is available to all Steemians.
A source of up to date general information and tools for every Steemian wanting to keep up with what is happening.
Especially helpful in the daily tracking of witnesses.
Thanks to: @drakos (Witness)