For example if I want to exchange some Ltc for bitbtc with some one is it possible to create a smart contact to track the transaction on a block explorer and once It find that the Ltc arrived at my address automatically release the bitbtc to the other party?
This would make great benefits to the dex
In general, you can just place an order on the market: https://wallet.bitshares.org/#/market/BTC_OPEN.LTC
For swapping, you can watch this: https://github.com/bitshares/bitshares-ui/issues/866
About escrow and OTC service, will be discussed in this ticket: https://github.com/bitshares/bsips/issues/44
This is currently not possible. (Using OPEN.LTC or an escrow works, but is not trustless.)
Atomic Cross-Chain Trading is the important buzzword here, but it doesn't look like this is going to be implemented soon.