Is there an app that can open files without extensions?

any program can open files without extensions. extensions are for Windows users to double click to open them with a program of choice.

as long as the file is the right format, Word, for example, can open a Word document even if it has no extension.

of course, you cannot always open any file. each different file type requires its own program to open it.

also, Mac files won't always open on Windows, as Windows cannot run Mac programs, and vice versa.

so you need to know what type of file it is first, or at least what program created it.

where did it come from? if someone emailed it to you, ask them what program they used, and ask if they can save it in a format you CAN open.

Try opening the drive in the safe mode

manually enter .txt at the end of the file and open it. skim the text file for any patterns or phrases that might tell you what it is and what the extension should be. i'd also try dragging and dropping it into vlc.

odds are those are all just test files added to the card. my guess would be it's from H2testW being used to test if the card capacity is legitimate or counterfeit. those can be deleted. 

my other guesses are that those are deleted files in a "recycle bin" on your sd card. not sure if any OS or app does that but that's where you'd see random characters usually with the same prefix. alternately, i'd suspect drive corruption. you can run the card through check disk in windows: run>cmd>chkdsk>D: /f ("substitute "D" for whatever your drive is. the /f will attempt to fix any detected errors on the disk). 

beyond this, if you don't know what it is you probably don't care enough about the contents for them to actually be worth saving.