STOs and IEOs are alternative token sale models that emerged after ICOs started to fade in popularity. IEO stands for Initial Exchange Offering. IEOs share a lot of similarities with ICOs. They are both largely unregulated token sales, with the main difference being that ICOs are conducted by the projects that are selling the tokens, while IEOs are conducted through cryptocurrency exchanges. Cryptocurrency exchanges have an incentive to screen projects before they conduct a token sale for them, so the quality of IEOs tends to be better on average than the quality of ICOs.