Right now, Tezos — a blockchain startup you've probably never heard of — is raising money through an initial coin offering, or ICO. Tezos has raised $206 million in about four days, and the sale is scheduled to continue for eight and a half more days.

At this rate, raising half a billion dollars is not unimaginable.

Unlike many other recent ICOs, Tezos is not based on Ethereum. Instead, it operates on an entirely new blockchain, a "self-amending cryptoledger" that rewards developers who upgrade the network's protocols and allows for "seamless," consensual upgrades of those protocols (read the white paper here for a lot more detail). This makes it a competitor to Ethereum.

Tezos tokens, Tezzies or XTZs, can be purchased with both Bitcoin and Ethereum. And purchased they are: At the time of this writing, Tezos has raised 52,795 BTC and 269,118 ETH, for a total of over $206 million at current prices. This already makes the Tezos ICO the largest in history (overshadowing the recent Bancor ICO, which raised $153 million, as well as the EOS ICO, which raised $185 million in five days).

Here's another important point: unlike many recent ICOs, the Tezos ICO is uncapped, meaning there's no upper limit of funds the company can raise. The only limit is time, and with approximately 8 days and 14 hours to go, the ultimate amount Tezos will raise will likely be a lot bigger than it is now.

Of course, the interest may wane in the coming days, and the ultimate amount Tezos will raise depends on the highly volatile Bitcoin and Ethereum cryptocurrencies. The price of both BTC and ETH has fallen considerably in the last several weeks; if they were anywhere near their all-time highs (which they were around the time of the Bancor ICO), Tezos would already be sitting on more than $250 million.

Tezos has more than a few similarities with Bancor. Both startups are incredibly ambitious, with intent to change the cryptocurrency landscape forever. Some hot names are on both companies' teams; for example, venture capitalist Tim Draper has invested in both companies. And both companies have been criticized in the cryptocurrency community for letting their fundraisers collect insane amounts of money.

It's crazy how many worst practices Tezos has incorporated into its crowd sale yet people still give them money — Evan Van Ness (@evan_van_ness) July 1, 2017

I will not be participating in the #tezos #ICO tomorrow. Most ridiculous ico I've ever seen. Think twice and do the research b4 investing — Max Kaplan (@maxekaplan) June 30, 2017

It might sound counterintuitive to limit a fundraiser in order not to raise too much money, but it is worrisome to see startups that have barely launched their first finished product raise hundreds of millions of dollars.

"Tezos (...) do have a solution that could mitigate some of the issues seen with other blockchain tokens through their governance model," Charles Hayter, CEO of CryptoCompare, told Mashable in an emailed statement. But he, like many others, warned that uncapped ICOs are problematic.

"ICO's which are uncapped are dangerous as they imply and show a complete disregard for corporate discipline - and to an extent an element of disrespect for the investor. The question that needs to be asked is can the job be done with less money (...) and that throws a spotlight on the fairness & truthfulness of the proposition being offered," he said.

Despite the criticisms, Tezos' ICO is proof that token crowdsales are still incredibly hot, both for traders looking to earn a quick buck by flipping new tokens and for crypto-related startups looking to get funded. Over-the-roof valuations will make it increasingly hard for these crowdfunded startups to prove their worth, and it feels like some sort of crash is inevitable, but it hasn't happened yet.

Mashable has contacted Tezos for comment and will update the article when we hear from them.

Disclosure: The author of this text owns, or has recently owned, a number of cryptocurrencies, including BTC and ETH.