Most paper developers are used as one-shot after dilution. The classic Dektol, for instance, is mixed from powder to make a stock solution for storage, and then the stock solution is diluted 1+2 or 1+3 just before use, and discarded after the printing session (if a lot of prints are being processed, it may become exhausted and need to be replaced sooner, of course, but a liter of working strength Dektol is good for twenty or so 8x10 prints).
There are commercial paper developers that are sold at higher concentrations, of course -- seems to me someone mentioned one that goes 1+9 for prints just the other day. Kodak used to also sell a developer very similar to Dektol known as MQ Universal in single-use packets; one packet would make enough paper strength developer to fill a 4x6 tray for contact prints, or enough to fill a daylight tank at higher dilution for developing film. Ilford also sells chemicals in what they call "sachets", sized for a single use, mix, use, and toss -- it's an expensive way to work, but everything is fresh every time. I don't know, however, if that includes a print developer.