If the opponents interfere over our 1N opening bid, we have the following agreements:

Over direct doubles:
New suit bids are natural and weakish, showing 5-card suits.
A pass suggests opener run, by bidding a 5-card suit or redoubling
with none.
Redouble shows that it is our hand. We will double them or
declare. If the opponents run and we can't double,
Rubensohl is on.
2N is game-forcing and very unbalanced.

If opponents double in the passout seat, a redouble by opener shows 4 spades. Redouble by responder is SOS.

Simple natural overcalls, or two-suited overcalls where only one suit is known (e.g. Brozel 2S, Astro 2C):
Double is penalty-oriented. Texas transfers are on. All bids through 2S (except a cue-bid of their suit, if available) are natural signoffs. Bids from 2N to 3H are transfers to the next suit. If the transfered-to suit could have been named at the 2-level (e.g. 1N-2D-3D) responder shows invitational or better values and opener should take positive action with a maximum or a big fit.

When opener accepts the transfer:
New suits are natural and forcing.
3N tends to show a stopper and is choice of games. A transfer to opponents' suit is game-forcing Stayman. If opener does not have a fit, he accepts the transfer without a stopper, and bids NT with a stop. If no stop is ascertained, the bidding can stop in 4m. If opponent's suit is a minor, there are some complications.
3S shows a raise to 3N without a stopper.
3N promises a stopper.
If available, a cue-bid of opponents' suit at the 2-level (e.g. 1N-2C(Astro)-2H) is a weak takeout, ostensibly 3-suited.
Two-suited overcalls, both suits are known (e.g. Brozel 2H, Landy):
The structure is similar,with the following modifications:
If there is one cue-bid available at the 2-level (e.g. 1N-2H(Brozel)-2S), it is a weak takeout for the other 2 suits.
If there are two cue-bids available, (e.g. 1N-2C(Landy)-2H or 2S), the cheapest is a weak takeout, the other is the equivalent of a natural raise to 2N.
There will be two "transfer cue-bids" at 2N or higher.
The cheapest is game-forcing "Stayman".
With no fit, opener bids 3N with both enemy suits stopped, otherwise cue-bids the cheapest suit in which he lacks a stopper. If he makes the cheapest cue-bid, responder counter cue-bids to promise a stopper in the cheap suit, deny one in the expensive suit.
The other transfer cue-bid is a raise to 3N lacking a stop in the expensive suit. Opener accepts the transfer holding a stop, and denying a stop in the cheap suit. He bids 3N with both suits stopped.
3S is a raise to 3N promising a stop in the expensive suit and denying a stop in the cheap suit.
3N shows stops in both enemy suits.

An example: After 1N-2D(red suits)

double= penalty
2H= weak takeout for the blacks
2S= signoff
2N= transfer to 3C
3C= Forcing Stayman. Without 4 spades, opener bids 3N with the reds stopped, 3D with diamonds unstopped (responder bids 3H to ask for a heart stop) and 3H with a diamond stop and hearts unstopped. The bidding can die in 4C if 3N is unplayable.
3D= Raise to 3N with no H stop. May or may not have a diamond stop. Denies four spades. Opener bids 3H with a H stop and no D stop, and 3N with both suits stopped.
3H= Transfer to spades, invitational or better.
3S= Raise to 3N, H stop, no D stop.
3N= signoff
4C= Gerber
4H= Texas

When opponents have shown one or both minors (e.g, 2m natural, 2C=minors, 2C=clubs and another suit), there might be some problems when responder has one major, opener the other, and stoppers in the enemy suit(s) are not specified. We use the following structure:
1N (2x-showing clubs) 2N:

3C= no club stop, may or may not have a 4-card major; bid 4-card majors up the line.
3N by opener is neutral, just showing no major fit.
3N by responder shows a club stop.
If no fit is found, the 3D= club stop, no diamond stop. Now bid 4-card majors up the line, with the obvious provisions.

Other bids= as above, show stops in both minors.
Other special agreements:
Over 2C=1 mystery suit (as in Cappelletti):
double=Stayman, system on.
Over transfer overcalls:
double: values, no clear direction.
bid their suit: weak takeout.
pass, then double the accept: penalties.
All the rest of Rubensohl is on, as if they had bid their suit naturally.
Over Crash double: system on
Over Crash 2C: double is Stayman, system on.
Over Crash 2D:
double: Stayman.
2H,2S: signoffs.

2N shows clubs, 3C shows diamonds.
3D and 3H are transfers, invitational or better.
3S is Minor Suit Stayman.

bidding can stop at 4D.
3D= 1/2 club stop; now bid 4-card majors up the line.
3M,3N= natural, show a club stop
4m= both majors, maximum, concentration of strength.
4H= both majors, maximum, no concentration of strength in the minors.

1N (2x-showing diamonds) 3C:
3D= no diamond stop, now bid 4-card majors up the line. other bids from 3H to 4H= as above.
1N (2x-showing minors) 2N

3C= no club stop.
3D = club stop, no diam stop. Now bid 4-card majors up the line.
3N by opener shows a diam stop. 3N by responder is neutral.
3M= natural, no club stop or both minors stopped (bid 3N later if no fit is found)
Source: Paul Glick