Oh, I always wanted to use 4gb of RAM to add files to Git.
I know hating Electron apps is the new fad, but it would be nice to check the facts before you grab your fork.
My guess is that compared to Slack, Github app doesn't really do much when idle. Slack fetches user statuses, new messages, notifications and so on. When you have an open channel with ongoing conversations that will add up in the RAM. This app doesn't seem to do anything when idle, so the RAM usage doesn't increase.