Weak Notrump Opening
Virtually every decent bridge player plays Weak-Two (of a suit) opening bids. Opening 2 of a suit with 6-12 HCPs and a 6-card suit accurately describes your hand for partner while taking a lot of bidding space away from your opponents..
For some reason, the vast majority of people who play Weak Two bids do not play Weak Notrump bids despite the fact that they have the exact same advantages.
There is some debate about whether or not to play transfers in WNT. The usual argument for transfers in strong NTs is that it lets the stronger hand be declarer. This is not as significant in WNTs where responder could easily have at least as many points, or even more, than opener. Another benefit of not playing transfers is that it leaves 2 available for game-forcing Stayman.
3 can be used as forcing in reponse to 1NT. Opener raises with 3 of the suit and otherwise bids 3NT.