

Read-only, or the ability to edit filenames & upload files?
Read only: as per other answers here, basically any HTTP server. The easiest one I know would be darkhttpd, because it requires no config files and can be run without root.
Read write: I like WFM https://github.com/tenox7/wfm
Direct metal liquid contact from pin to pin! I love it.
(Not to mention how satisfying it is to get a pile of undamaged ICs after recycling)