I have a mobile phone used only for RadioPlayer and TuneIn radio.

Wondering: is there a free app that will play music from a shared folder? (hard drive connected to router)

Android 2.3.7

Majority of music is in Flac format.

I would also like to know an iOS alternative if anyone would mind

Try the VLC app - it supports media streaming and many formats so worth a look at least. From a "dumb" hard drive on the network without a media server I'm not sure what joy you'll get.

I have a NAS drive which is probably the way to go in the future as they have media servers for just this purpose and are getting much cheaper.

Manufacturers also generally provide apps (I have a Western Digital app for my Android devices). My NAS uses Twonky media server but I haven't tried the Twonky Media Android app (also available on iOS I presume) yet.

Can't you just use ES File explorer to view the share and then just click play and it'll play in whatever player you choose.

This works for me too though it's not particularly convenient.

VLC is not supported by phone, but will give ES File Explorer a go.

Thanks!