I've heard of other cryptos such as Litecoin. I was wondering how are they similar/different to BTC? and if their are any other cryptos that are worth looking into?
nearly each one has a different approach.
namecoin is a merged mining cryptocoin. thus its protection from a 51% attack comes (mostly) from bitcoin miners who mine namecoin with no additional work performed.
ppcoin has a proof of stake. this is a different type of protection from a 51% attack where those who already have coins have a say what a block includes, and not just the miners.
litecoin is a proof of work cryptcoin, but it uses a different algorithm for the mining work. it uses scrypt instead of sha256 and since scrypt uses a lot of memory, there are no fpga devices for it (yet, maybe?) and definitely no asics for it.
consider all the worry about a "lot of computers" hurting bitcoin, and litecoin has just like 2% of the amount of mining (protection) that bitcoin does, and even fewer nodes. there are a lot of unused gpus around now that could be used against litecoin and exceed that 51% threshold. there isn't much of an economic reason to do so. if you were to sell litecoins at the exchanges like btc-e, vircurex and others for some bitcoins, this 51% could then double spend those ltc deposits to the exchanges, but what could you buy using those litecoins after?
if litecoin were to be 51% attacked, there's nobody that would take those litecoins after the attack. so litecoin is pretty vulnerable to a 51% attack (relative to bitcoin) yet but it hasn't had that happen yet and who knows if anyone ever will.
