HAF is a framework for building apps, but it is quite different from Flux/React, because flux/react is focused on simplifying creation of frontend apps, whereas HAF is focused on building backend apps that can easily process data from the Hive blockchain. In other words, you can build a dApp where the backend is based off HAF and your frontend UI is built on React/Angular/Flutter/etc.

HAF defines a way to easily build and manage SQL tables with processed forms of the blockchain data. The very base level of HAF does the job of injecting raw blockchain data into a SQL database and managing database reversions automatically in the case of a fork.

HAF will come with optional sets of pre-written code to do things like creating tables with Hive account data and APIs to manipulate those tables.

Our 2nd layer smart contract engine needs a way to efficiently get the raw blockchain data into its database and manage state changes in the case of forks. HAF will do all this work for it. And some of those optional pre-written modules for maintaining additional tables (such as a table of Hive accounts) will also be useful to the smart contract engine.