What is MetaMask Flask?
MetaMask Flask is a distribution of the software designed for developers. It's like a laboratory (hence the name) where the MetaMask team can try out new ideas and features. It has experimental, even dangerous functionality in it that is not meant for everyday use. It also doesn't have the same stability guarantees that the production distribution of MetaMask has.
Why was it made?
Most of us think of MetaMask as the fox-themed software that lets us access all the cool stuff happening in Web3. One of the reasons that MetaMask works as well as it does for users is that first, it works well for developers. It's easy to integrate MetaMask into your dapp or blockchain-enabled website.
MetaMask has always had this focus on developer experience, and the community has responded in kind. In fact, there are so many suggestions and requests for features that the development team can't keep up with vetting them all, and deciding between the competing options. At the same time that the product gained popularity with developers, it was exploding with end users, and was maturing overall. As more value came into the crypto ecosystem, it became more and more important to have a secure, stable production version of MetaMask, and so the decision was made to make a separate, "test environment" version of the application: and Flask was born.
What can you do with it?
The first big feature shipped through Flask has been MetaMask Snaps. Snaps is a whole topic in and of itself, but think of it like this: Snaps allows developers to bring any kind of functionality they want to the application. Given how broad that is, and the potential security implications, snaps can only be used in Flask at the moment; however, the plan is to allow users to customize their MetaMask experience through this functionality.
How do I get involved?
If you've got the technical understanding, check out the Snaps documentation here, and you can download and install Flask here. One thing to keep in mind: you can only have one installation of MetaMask active at a time, so if you're going to be using Flask, make sure your production MetaMask is either disabled, or you're using a separate browser profile entirely.