Hello, I am knowledgeable.
When you connect to an Open Transactions server, you can do all the same basic functions online that you might do at the bank... Open an account, write a cheque, deposit a cheque, purchase a cashier's cheque ("voucher" on OT), withdraw cash, and deposit cash.
You can also issue new currencies (upload the currency contract and the server will give you an issuer account.)
You can also define basket currencies (and exchange in/out of them.)
There are also payment plans and markets (with trades.)
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If you wanted to issue a Bitcoin-backed currency, then you would draw up a currency contract stating this, and upload it to an OT server. After that, any other user can open accounts denominated in Bitcoins (or whatever you call your currency.)
From there, you can write cheques, withdraw in untraceable digital cash, do deposits, trade on markets, form basket currencies, etc all using that new Bitcoin-backed asset type.
You could also issue 4 or 5 other different currencies on the same server, and users could trade them against each other on markets.
Here is a diagram, if it helps:

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The various instruments that you see on Open Transactions DO have expiration dates.
-- Cheques have expiration dates set by the writer.
-- Cashier's cheques have expiration dates set by the server.
-- Cash notes have revolving expiration dates according to the terms of the appropriate contracts. (If cash notes did not eventually expire, then the spent token database would have to grow forever, which is not feasible.) Wallet software will need to automatically exchange tokens before they get too close to their expiration dates.
-- Trades and Payment Plans also have date ranges as well as other rules about how and when they process.