When you need to quickly create a to-do list and share it with others, Flask can help you out. Just go to the site, start adding items, click share, and send it to whomever you wish.
Flask works in pretty much any modern web browser and adapts to your mobile phone, too, so you can create lists anywhere you're connected to the internet. Without an account Flask only supports creating one list, but if you want to make multiples you can do so by signing up. That's all Flask does at the moment, but it's a great way to create and share a to-do list quickly when you need one.