Amaze File Manager is a free and open source file manager for Android with zero in app purchases.
Ranked in these QuestionsQuestion Ranking
Pro Material Design and fast operation
Amaze File Manager follows the Material Design guidelines as well as operates very fast.
Pro Open source
Amaze File Manager is an opensource file manager.
Pro Only file browsing
Doesn't try to do everything, so it remains light (no incurred battery usage) and doesn't pollute your Intents with new ways to open your images or audio files but instead uses your already set up default applications for that.
Con No networking tools
Sadly there are no networking tools built into Amaze File Manager.