The EOS ICO was unique and deserves a special mention. The concept was that one billion EOS tokens were to be distributed over a period of 341 days. 200 million or 20% were distributed during the first five days, from June 26, 2017, to July 1, 2017, and an additional 700 million EOS tokens were distributed in two million blocks every 23 hours thereafter. 100 million or 10% was reserved for Block.one, an open source software publisher specializing in high performance blockchain technologies (https://block.one/about/).
Note that the vesting period of the 100 million for Block.one is 10% over 10 years. At the end of the five-day period and at the end of each 23-hour period, a fixed number of tokens were distributed proportionally amongst all the investors, based on their contributions. In other words, everyone in a specific period gets the same amount of EOS per ETH as everyone else. You only know for sure exactly how many EOS you are getting for your sent ETH once the period...