Musicolet. It's a free music player app. It let's my organize all my music (downloaded onto my SD card) and play it without ads. I ended up spending $5 to get the premium version for crossfade and other features. Originally found it after my student discount spotify +Hulu plan ran out. I canceled spotify and use the lowest tier of Hulu ($2.15 per month with a student discount) now. Way cheaper than paying $10+... Source: 6 months ago

KitKat was so good that I'm still rocking it on a NoteⅣ for offline maps and music in my car even though there are newer official updates available from Smasnug: https://i.imgur.com/AhYJSYP.jpg The newest version of Musicolet still supports it! https://krosbits.in/musicolet/. - Source: Hacker News / 10 months ago

Yeah I do similar, I actually use musicolet to listen to my offline music library (https://krosbits.in/musicolet), an android app that is just offline, no ads, no network permission at all, nothing. It does the job very well and it does not mine any data or show any ads. I highly recommend to give it a try (I assume you use android?). And to add, while it is free and I could have continued just fine not paying... - Source: Hacker News / about 1 year ago

Musicolet is hands down the best music player I've found on Android and it's fully featured for free https://krosbits.in/musicolet/. Source: almost 2 years ago

I use Musicolet for Android (https://krosbits.in/musicolet/); so far the most complete music app. Source: almost 2 years ago

If you have a PC Wondershare has a product called MobileGo. It's free functionality is limited but it does have a simple file structure navigation portion included in free, it's very useful. You hook the FTVS to your PC using the power cable and it becomes a jump drive. Source: about 3 years ago