[Free]

Basicly, it uses 2-suited overcalls with 4-4 or better. Overcalls in a minor are sacrificed for this, and moved to 3m. However, the competitive bidding improves because partner can usually support preemptively quite fast, or explore for game using a relay. To make the overcalls limited, you need a powerdouble, which is probably the biggest disadvantage of all...

The 1♣ opening is a little different than the others:
(1♣) - ?
Dbl = 15+hcp, any
1♦ = 5+♥
1♥ = 5+♠
1♠ = 4+♠ and 4+♦
1NT = 4+♥ and 4+♦
2♣ = 4+♠ and 4+♥
2♦ = (5)6+♦
2M = weak!
2NT = weak with 55+ lowest unbid suits (this can be changed to a 3-suiter with short ♣)

(1♦) - ?
1M = 5+M
1NT = 4+♥ and 4+♣
2♣ = 4+♠ and 4+♣
2♦ = 4+♠ and 4+♥
2M = weak!
2NT = weak with 55+ lowest unbid suits (this can be changed to a 3-suiter with short ♦)
3♣ = 6+♣ (constructive)

(1M) - ?
1♠ = 5+♠
1NT = 4+♦ and 4+♣
2m = 4+OM and 4+m
2M = 3-suited with short M
2♥ = (5)6+♥ (after 1♠ opening)
2♠ = weak! (after 1♥ opening)
2NT = weak with 55+ minor
3m = 6+m (constructive)

So basicly:
1x-1NT shows lowest unbid suits
1m-2m shows both Majors
1M-2M shows 3-suited hand
2m overcalls are natural with a side Major

After 2-suited overcalls with a M, you never have a good 5 card M (otherwise you just overcall 1M)

[Gerben42]

Thanks!