m is no longer backed by any external currency - it is merely the game currency to buy ingame items. The CK shares were turned into m.
m3 is backed by XMR
b1 is "supposed to be" backed by BTC
e1 is "supposed to be" backed by EURO
...
What does "supposed to be" mean?...
It means a high probability of a fractional reserve. There are not enough XBT to back all the b1 or EUR to back all of the e1. This is combined with a form of exchange controls. EUR withdrawals are only allowed in cash in person in Tallinn Estonia, XBT withdrawals are subject to certain delays unless one pays a premium for a faster withdrawal (B2). I posted on exchange controls in this post
https://bitcointalk.org/index.php?topic=1850565.msg18633169#msg18633169 and the distortions this creates in the marketplace on this post.
https://bitcointalk.org/index.php?topic=1850565.msg18616745#msg18616745