blockchain_follower is a skeleton application which contains all that you'll need to write a simple application which follows the Helium blockchain. All you'll need to do is clone it, do a whole-repo search replace for blockchain_follower => my_app_name, open bf_follower.erl and look for the TODO comment. If this doesn't work, or you don't understand the comment says, please open an issue on the Github repo.
This repo is permissively licensed, so you don't need to tell us what you're doing with it, but we would love to know if you'd like to share.
First, you'll need to have Erlang installed. You can use a later 21.x series OTP, or OTP 22+. Anything earlier is unlikely to work because of our use of persistent terms. You can also install rebar3 (see here for help with both), however we've included one here along with a basic Makefile to get you started. Once you have them installed, you can type:
$ make release
$ _build/default/rel/blockchain_follower/bin/blockchain_follower start
$ tail -F _build/default/rel/blockchain_follower/log/console.log
Within a few minutes, you should see the chain begin to sync. After it has synced up to the assumed valid height, it will begin to apply all the blocks, and you'll see the code in bf_follower.erl's add_block handle_info clause start to fire. After the sync, it will continue to sync the chain until it's up to date with cluster gossip. Every time it appends a block, it will fire that handle_info clause.