Please take a look at the topics if anything is useful for you.
If you are not actually working ON Flowee, you may be searching for the API docs;
The Hub API documentation is for developers writing tools. Please see API docs for more.
The Hub is not a new codebase, it in fact is the same codebase that Satoshi originally wrote for Bitcoin in 2008-2011. Back then it was written to be everything in one product. Flowee realized that a product that tries to do everything will end up not being very good at anything.
The hub is what is left, we kept all the validation, the mempool and deprecated the creation of transactions (the wallet) and other parts which make little sense for most users.
As a result of deprecating things like creation of data we now can fully leverage the benefits of blockchain technology. It is read-only by definition.
We added memory-mapped blocks, which drastically reduces memory usage and loading times. This then lead to the ability to make Flowee massively parallel enabled. If you have a machine with multiple cores, we actually use them. Details are in the multi-threaded design documents. This is used for the validation engine, as well as for the network manager.
Less exciting but extremely useful is that the logging framework has been greatly upgraded, compared to the rather weak and single-minded version that the competition uses there is actually a rather large advantage there.
Operators and developers will want to read the logging levels guidelines to get the best out of the system.