Bitcoin, the digital currency that has exploded in popularity over the last few years, is going through a tough time. China is cracking down on the currency, forcing one of the country's biggest exchanges to stop accepting new deposits this month. Bitcoin's defenders are being hounded by U.S. feds. And the volatile currency has plummeted to less than half the value it had a few months ago.

But just because Bitcoin is under attack doesn't mean that digital money is dead. In fact, new currencies are popping up like daisies. There are about 290 currently in existence, and the very first CryptoCurrency Convention is taking place on April 9. If Bitcoin stumbles, this could be their big opportunity to shoulder into the global market... or at least annoy Kanye West.

As my colleague John Aziz notes, "These currencies will not see the same kind of price appreciation that Bitcoin has enjoyed. But they will avoid the volatility produced by profit-hungry speculators, which may well be key to gaining more mainstream acceptance." Without further ado, here are nine digital currencies you should know about:

Aphroditecoin

After Cyprus' economic crisis in 2013, Bitcoin boomed and there was talk of Cyprus getting its own Bitcoin ATM. But in February, Cyprus' central bank criticized the currency, warning buyers that it's a risky investment. Aphroditecoin has now stepped in, with the aim of becoming the main cryptocurrency for Cyprus. On April 21, the makers plan to give 885,000 Cypriots 25.4 Aphroditecoins each, as a gift. (See also: SpainCoin and GermanyCoin.)

Dogecoin

Dogecoin was born after a marketing specialist and a programmer got together to join two trends that were lighting up the internet: Bitcoin and the "doge" meme. (To understand doge, click here.) Dogecoin quickly became very popular. Before the Sochi Olympics, the Dogecoin foundation raised almost $25,000 in 12 hours to send the Jamaican bobsled team to the Games.

DopeCoin

Unlike PotCoin, the developers of DopeCoin market this currency to both legal and illegal drug buyers, from the black market to Overstock.com, according to the Huffington Post. The coin's founder, "Dopey," told the news outlet, "We're the bad boys of cryptocurrency."

Litecoin

Litecoin is "one of the more serious altcoins," according to Forbes, and often draws comparisons to Bitcoin. Litecoin has some technical differences, including faster transaction rates, and has been nicknamed "silver" to Bitcoin's "gold." Litecoin is one of the currencies that the Target credit card thieves were willing to accept as payment for hacked financial details.

Murraycoin

Murraycoin is a tribute to actor Bill Murray. A portion of Murraycoin's pool fees are donated to the Murray Bros. Foundation, the actor's charity, which donates to organizations like the Firehouse Subs Public Safety Foundation. The developers claim that the currency has a transaction rate that is six times faster than Bitcoin's.

PotCoin

Legal marijuana dispensaries in states like Colorado and California largely operate as cash-only businesses, because banks won't work with them. This makes them hot targets for theft. The developers of PotCoin hope that these legal businesses will switch to their digital currency. So far, several marijuana businesses have signed on.

Sexcoin

Sexcoin is marketed, no surprise, to the sex industry. The developers hope that adult-content consumers, performers, and producers will use the cryptocurrency to make anonymous transactions. "Gay, straight, male, female, or trans, Sexcoin seeks to solidify and progress a community of open-minded free thinkers," the developers say. To date, the list of companies accepting Sexcoin is pretty short.

SiliconValleyCoin

SiliconValleyCoin is marketed to people who work and live in Silicon Valley, Calif. The developers say they launched the coin because "we want every single employee at these startups to not only know about cryptocurrencies but to have an incentive to incorporate our industry with theirs." On April 25, the developers plan to start mailing the coins to certain ZIP codes near major tech companies in the valley.

TittieCoin

TittieCoin is a cryptocurrency that's illustrated with — uh, you can figure it out. Besides being used for transactions, this small cryptocurrency aims to raise money for breast cancer research and charities.