*** Sorry, just realized you wanted an online board.
This is for your computer but it has a portable version so you can put it on a usb key and take it with you. The other good thing about it is that you can save the games after you replay them and start building your own db.
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Try Scid:
I'm reading some chess books and they go over a particular opening but then discuss the other lines rather than just the main. I'd like to find a board that will allow me to input the moves and explore the rare variations and then quickly go back to the main line to keep going along with the book (i really need to see the board set up to follow). The board on this site doesn't seem to let me go back a move or replace pieces, unless there is something I don't know. Anyone have a reccomendation?
edit: also the board on here doens't seem to let me flip the position and I'd like to look at it from black perspective