Andrei's preferred system

Offensive

• Natural, 5 card Majors, opening may be light in third seat (with reversed Drury).
• Strong 1NT (15-17 hcp) w/ Stayman and transfers (optionally including to minors: 2S for clubs, 2N for diamonds)
• Checkback Stayman (aka Roudi)
• Weak two's (2D/H/S) with Ogust.
• 2C is strong (23+ HCP...) with natural responses
• Gambling 3NT (w/o exterior stoppers)
• Splinters, control-showing CBs
• Gerber (after NT)
• Roman KeyCard Blackwood (with 30 - 14 - 2 with Q - 2 w/o Q responses)
• 4th suit forcing
• raises are preemptive rather than inviting (see The Law)

Optional:

• Bergen raises
  
• Super-accepts on NT transfers
  
• Support X/XX.
  
• 2-way drury (2C with 3 cards, 2D with 4 cards)

Competitive

• DONT over opps' NT opening
• negative doubles up to 3S
• Unusual 1NT/2NT (showing the lowest two remaining suits)
• Michaels CB (showing the highest remaining suit plus another one)
• jump-shifts promise fit (see The Law) and the respective suit.

Leads

• A from AK asks for preference, K from AK asks for card count
• Up-low from dblton in pd's suit
• Low from under a honor in 3 in pd's suit
• m-u-d from 3 small cards against suit, top of nothing against NT
• Top honour from a sequence

Signals