user324: I'm seeing lots of bitcoin-esque alternatives mentioned here. What alternatives exist and how do they differ from Bitcoins?

user3712: The best competitor is probably ppCoin (PPC) http://www.ppcoin.org.  I'm surprised it has not been mentioned.
ppCoin has a lot of advantages over bitcoin, including:

power efficiency

BTC currently uses more power than a nuclear reactor, which is a horrible shame [check the power stats on blockchain.info and compare them to the output of Three Mile Island (wikipedia)]
However, PPC uses proof-of-stake mechanism, which means the network can survive (and grow) without burning up CPU/GPU/ASIC cycles.
Bitcoin's power problem won't end with ASICs.  Soon everyone will have tons of ASICs using just as much power.  BTC will always use the max power that is profitable.  The more BTC is worth, the more power will be used.  This is scary and bad for the environment.

security enhancements

proof-of-stake secures the network if mining decreases in long term when little new money is created
in BTC when mining ends transaction processors are incentivised to compete for transaction fees, which means ignoring each other's verified transaction blocks.  This can lead to destruction of the network.  PPC solves this by destroying transaction fees and simply providing incentive trough mining.
N.B. Some will say that PPC is  not decentralised because its checkpointing process is centralised, in that the PPC developers add checkpoints with each release of the official PPC software.  However, this is a fallacy.  Bitcoin uses the same type of centralised checkpointing mechanism, i.e., through the released software.  Thus, PPC is no worse than BTC in this regard.  Decentralised checkpointing is a hard problem.  There is an interesting paper "Bitter to Better" by some folks at Stanford suggesting a better decentralised checkpointing mechanism.

mechanisms to encourage actual use of the currency and survival of the network

mining is always encouraged (mining is always profitable, even in the long term)
transaction fees are not collected by transaction processors, but destroyed in order to counteract the currency created by mining.
Thus, the money supply should remain constant (after it reaches a certain point)


The last point is really relevant because bitcoin users tend to horde than spend.

ppCoin mining pool: ppcpool.bitparking.com
ppCoin exchange: ppcexchange.bitparking.com

It's profitable and you can mine a lot of coins quickly, but most importantly there's a lot of long-term potential for growth.

user1870: There is also TimeKoin; see www.timekoin.org

5 minutes per block; twice as fast as bitcoin
No pre-mined coins.
Does not waste CPU cycles for minting coins. Coin minting is controlled by time.
Each coin is indivisible; so each TimeKoin is like one Sathoshi.
Currently only 450,000 coins in existence.


user153: Currently the most comprehensive list is curated here:

http://bitcointalk.org/index.php?topic=134179.0


user323: There are a number of other cryptocoins in use alongside Bitcoin, the most notable are:

Testnet Bitcoins (used only for testing Bitcoin applications, but they are an important mention) - they work exactly the same as Bitcoins.
Namecoins - coinage used as a distributed naiming system blockchain. Their most notable feature is that they can be merged mined with Bitcoins.
LiteCoins - "silver to Bitcoin's gold" - their blocks are generated every 2,5 minutes, and their hashing algorithms are more CPU-friendly (mining with graphic cards doesn't work well with those).
SolidCoins - 2 minute blocks, there isn't a limit on how many coins will be generated, CPU friendly, difficulty is adjusted more often, close-source. The SolidCoins have undergone a "reset" recently and have earned themselves a negative reputation for how some issues were handled.
GeistGeld - 15 seconds blocks, making it the fastest alternative crypto-currency.
I0coin - they don't list any difference from Bitcoins on their website
Ixcoin - same parameters as Bitcoins, asides more coins being generated each block (thusly, all 21M coins will be generated sooner)
Tenebrix - CPU friendly, a few million coins pre-minted

A list of them is also maintained on the Bitcoin Wiki.
There is a relative ease in creating new cryptocoins, as you can just tweak the main client, encode a new genesis block and start your alternatives with small effort.

324: <p>I'm seeing lots of bitcoin-esque alternatives mentioned here. What alternatives exist and how do they differ from Bitcoins?</p>
 3712: <p>The best competitor is probably ppCoin (PPC) <a href="http://www.ppcoin.org" rel="nofollow">http://www.ppcoin.org</a>.  I'm surprised it has not been mentioned.</p>

<p>ppCoin has a lot of advantages over bitcoin, including:</p>

<ul>
<li>power efficiency
<ul>
<li>BTC currently uses more power than a nuclear reactor, which is a horrible shame [check the power stats on blockchain.info and compare them to the output of Three Mile Island (wikipedia)]</li>
<li>However, PPC uses proof-of-stake mechanism, which means the network can survive (and grow) without burning up CPU/GPU/ASIC cycles.</li>
<li>Bitcoin's power problem won't end with ASICs.  Soon everyone will have tons of ASICs using just as much power.  BTC will always use the max power that is profitable.  The more BTC is worth, the more power will be used.  This is scary and bad for the environment.</li>
</ul></li>
<li>security enhancements
<ul>
<li>proof-of-stake secures the network if mining decreases in long term when little new money is created</li>
<li>in BTC when mining ends transaction processors are incentivised to compete for transaction fees, which means ignoring each other's verified transaction blocks.  This can lead to destruction of the network.  PPC solves this by destroying transaction fees and simply providing incentive trough mining.</li>
<li>N.B. Some will say that PPC is  not decentralised because its checkpointing process is centralised, in that the PPC developers add checkpoints with each release of the official PPC software.  However, this is a fallacy.  Bitcoin uses the same type of centralised checkpointing mechanism, i.e., through the released software.  Thus, PPC is no worse than BTC in this regard.  Decentralised checkpointing is a hard problem.  There is an interesting paper "Bitter to Better" by some folks at Stanford suggesting a better decentralised checkpointing mechanism.</li>
</ul></li>
<li>mechanisms to encourage actual use of the currency and survival of the network
<ul>
<li>mining is always encouraged (mining is always profitable, even in the long term)</li>
<li>transaction fees are not collected by transaction processors, but destroyed in order to counteract the currency created by mining.</li>
<li>Thus, the money supply should remain constant (after it reaches a certain point)</li>
</ul></li>
</ul>

<p>The last point is really relevant because bitcoin users tend to horde than spend.</p>

<ul>
<li><p>ppCoin mining pool: ppcpool.bitparking.com</p></li>
<li><p>ppCoin exchange: ppcexchange.bitparking.com</p></li>
</ul>

<p>It's profitable and you can mine a lot of coins quickly, but most importantly there's a lot of long-term potential for growth.</p>
 1870: <p>There is also TimeKoin; see www.timekoin.org</p>

<ol>
<li>5 minutes per block; twice as fast as bitcoin</li>
<li>No pre-mined coins.</li>
<li>Does not waste CPU cycles for minting coins. Coin minting is controlled by time.</li>
<li>Each coin is indivisible; so each TimeKoin is like one Sathoshi.</li>
<li>Currently only 450,000 coins in existence.</li>
</ol>
 153: <p>Currently the most comprehensive list is curated here:</p>

<ul>
<li><a href="http://bitcointalk.org/index.php?topic=134179.0" rel="nofollow">http://bitcointalk.org/index.php?topic=134179.0</a></li>
</ul>
 323: <p>There are a number of other cryptocoins in use alongside Bitcoin, the most notable are:</p>

<ol>
<li><a href="https://en.bitcoin.it/wiki/Testnet" rel="nofollow">Testnet Bitcoins</a> (used only for testing Bitcoin applications, but they are an important mention) - they work exactly the same as Bitcoins.</li>
<li><a href="https://en.bitcoin.it/wiki/Namecoin" rel="nofollow">Namecoins</a> - coinage used as a distributed naiming system blockchain. Their most notable feature is that they can be merged mined with Bitcoins.</li>
<li><a href="http://litecoin.org/" rel="nofollow">LiteCoins</a> - "silver to Bitcoin's gold" - their blocks are generated every 2,5 minutes, and their hashing algorithms are more CPU-friendly (mining with graphic cards doesn't work well with those).</li>
<li><a href="http://solidcoin.info/" rel="nofollow">SolidCoins</a> - 2 minute blocks, there isn't a limit on how many coins will be generated, CPU friendly, difficulty is adjusted more often, close-source. The SolidCoins have undergone a "reset" recently and have earned themselves a negative reputation for how some issues were handled.</li>
<li><a href="http://www.geistgeld.org/get-started.html" rel="nofollow">GeistGeld</a> - 15 seconds blocks, making it the fastest alternative crypto-currency.</li>
<li><a href="http://i0coins.com/" rel="nofollow">I0coin</a> - they don't list any difference from Bitcoins on their website</li>
<li><a href="https://bitcointalk.org/index.php?topic=36218.0" rel="nofollow">Ixcoin</a> - same parameters as Bitcoins, asides more coins being generated each block (thusly, all 21M coins will be generated sooner)</li>
<li><a href="http://www.tenebrix.org/" rel="nofollow">Tenebrix</a> - CPU friendly, a few million coins pre-minted</li>
</ol>

<p><a href="https://en.bitcoin.it/wiki/List_of_alternative_cryptocurrencies" rel="nofollow">A list of them is also maintained on the Bitcoin Wiki</a>.</p>

<p>There is a relative ease in creating new cryptocoins, as you can just tweak the main client, encode a new genesis block and start your alternatives with small effort.</p>
