Most people who use Slack fall into one of two categories; You either think it's the best collaboration tool since email or you feel like a fire hose of chat messages and notifications is pointed at your face and you're just hoping someone will make it stop

Regardless of which group you fall into, it would be hard to deny that Slack has made a big mark in just five years. Today, more than 10 million users send messages every day, to the tune of over a billion messages a week.

Finally, after months of being one of the most highly anticipated public offerings, today is a big day for Slack. 

The company has filed to sell its shares to the public, starting today, at a price that would value the company at almost $16 billion. Instead of a traditional IPO, the company will instead bypass raising additional capital and avoid the high fees that come with underwriting banks and instead list its shares directly on the New York Stock Exchange under the stock symbol "WORK" at an anticipated $26 per share.

Whether you're a Slack user or not, here are three things to know about why it's a big deal:

1. Don't call it an IPO.

Normally, when a company goes public and files for an initial public offering, it involves investment banks who act as underwriters and divvy out shares. The company would issue new shares that are used to generate cash, and those would be what is primarily available to the public. That's not what's happening with Slack. 

Instead, Slack will list its shares directly with the NYSE. The shares that you'll be able to eventually trade aren't newly issued shares that generate money for the company, but rather are shares currently held by founders, employees, or investors. In fact, a direct public offering (DPO) is mostly a way for those insiders to unlock the value of their shares and generate cash. 

A byproduct of this setup is that shares might not be immediately available as the market opens since there is no large investment bank with millions of shares to offer to the public. Instead, shares will become available as those current shareholders decide to sell.

By the way, the fact that the company chose to go this route isn't just a cost-saving measure to avoid investment bank fees. It's also a signal--which leads to the next thing you should know.

2. $16 billion is a big deal. 

Even though Slack's choice of a direct public offering means it won't be raising any cash for its business, the reference starting share price of $26 means that the company would be valued at almost $16 billion. That's more than twice its valuation of $7 billion during its last round of investment. 

For a company that had just over $400 million in revenue in its past fiscal year and lost $141 million, the new valuation is a sign that both the company and investors are pretty optimistic about the future. That makes sense when you consider that most estimates are that Slack has as little as 2 percent of its potential market.

Investors have demonstrated that their appetite for tech company IPOs continues to grow, despite a few recent bumps for some big-name stocks.

3. A good sign for entrepreneurs.

Slack certainly isn't the first tech company to go public this year, and previous offerings have had mixed results. CrowdStrike, Fiverr, and Chewy all went public in recent weeks, and all have seen their share prices surge more than 50 percent above their initial offering price.

On the other hand, several recent public offerings haven't been as successful. Uber and Lyft, for example, both saw their share prices tumble below their opening. Uber has since recovered some, but Lyft's share price remains in the red.

But the most interesting thing for an entrepreneur is that with Slack, and Spotify previously, two of the largest recent public offerings by tech companies have been direct listings. That's a huge shift from the days when access to public markets was controlled exclusively by investment banks that ran the process and set share prices. 

Slack was in the enviable position of not needing to raise cash from its public offering and instead focused on making its existing shares available on the stock market. Companies are starting to see that "going public" has a new meaning for both founders and the market.