18Mag is set in the Hungarian half of the Austro-Hungarian Empire (or,
if you're Clare, in Rome or possibly in a hole).

You start with no money, but with some minor companies and major
company shares. In the initial draft you have a specific quota of
minors and major shares, you can't take 4 minors and 0 major
shares. Minors run trains and split revenue; they buy services (such
as trains) from 10-share major companies, which don't run
trains. Majors can still place tokens, which block routes but also
increase city values.

The stock market is one-dimensional. You drop one space on sales, gain
a space if sold out. Minors don't have a stock price, only majors.

Minor companies differ only in their starting hex and number of
"terrain tokens"; each terrain token means the bank, not the minor,
pays one hex's terrain cost. They all start with a 2-train and 50
forints.

Major companies differ in what service they offer to the minors. Their
Directorship works normally except that many of them will start the
game with no Director. Such a major always pays out completely.
However, once there is a Director, you can't sell shares to cause a
major to have no Director.

There are yellow, green, brown, and grey phases. One OR per SR in
yellow, two per SR in green and brown, and when the grey phase starts
the current OR finishes (even if it is the first of a pair), there is
one SR, three ORs, and the game is over. The bank is unlimited; there
is a forced phase advance mechanism which will always cause the game
to end.

You can lay or upgrade one tile, and lay a second yellow for 10
forints. Upgrades are permissive; if you can reach it, you can upgrade
it. Some tiles are double-sided, meaning the total available is shared
between two different tiles.

There's a terrain cost for upgrading OOs and B (Buda-Pest) from yellow
to green. F9 Lake Balaton is divided by the lake, which can never be
crossed; the tile mix means there's no way to build on both sides of
the hex.

Trains don't rust, but they can be "scrapped" (which actually returns
them to their major for resale); you would do this in order to buy a
bigger train. You have to scrap trains before you run routes. The
train limit is always 2. A train's size normally is the number of
cities and towns it can visit.

When an OO or B tile has two separate stations, a route can score them
both; Buda and Pest were two separate cities until 1873. In the brown
phase OOs and Budapest merge. You cannot run to or through a mine
(the grey 30/50 hexes) without buying the relevant service from a major.

Minors always half-pay.

All train types are available from the beginning of the game. There is
no obligation to own a train. There are 2, 3, 4, and 6 trains. The
phase advances when the first train is bought off the 3, 4, and 6
train stacks. If no train at all is bought in an OR, you put a marker
on the untouched train stack with the smallest trains; if it then has
3 markers the phase advances automatically (and I think this stack now
counts as having been touched; it won't advance the phase again if a
train is sold).

Major companies operate in descending share price order. They can
first place tokens, which block routes normally but also increase the
value of the city they are in (not the hex, in the case of two-city
OOs and Buda-Pest) by 10 forints.

Their only other activity is to pay dividends. They may pay out any
amount. Their share price rises (or falls) based on the dividend in a
way which is not related to their share price, only the absolute
amount of the dividend.

The major companies are as follows:

"Rail car" companies which give special powers to minors. Minors pay
for every OR they use the power, and the price increases both with
phase and if the minor buys the services of more than one rail car
company (eg one power: 10 forints; 2 powers, 30 forints; 3 powers, 60
forints). The power affects only one train. Anything shown as X/Y
changes between the green and brown phases.

RABA gives a 20/30 forint bonus for one offboard area.

G&C makes a train into a "plus" train; an N train can now run to N
towns and N more towns or cities.

SNW lets a train run to or through one mine, scoring it. It doesn't
count as a revenue location (either against the train's capacity, or
to satisfy the requirement that a route visit two locations).

Construction companies get money when construction is done. One gets
10 for any river or mountain hex (even if a terrain token is used, the
bank pays); one gets 10 whenever a minor lays a second yellow, and
half the cost of any token.

The two train companies get half the cost of any train bought from
them. The other half is paid to the bank.

The CIWL earns 30/50 forints whenever a route is run between two red
offboards, as does the operating minor (it doesn't buy a service, the
red-red bonus is just available if and only if the CIWL is in the game
- it's an optional new rule.)