WinBoard/XBoard should allow you to 'pause' the game by pressing the P button above the board. This stops the clocks and puts the engine in idle mode (possibly after it moved, if the engine itself does not support the 'pause' command). Pressing the button again then restarts the game.
I don't know if that is what you mean by 'adjourning'. If you want to really terminate the program and shut down the computer, WinBoard (and most other GUIs) would allow you to do this by simply saving the unfinished game on a PGN file. It will store the times remaining on the clocks as a comment in the PGN, and reloading the game should restore the clock times. (And even if not, you could always adjust the clocks to what they were when you stopped the game.)
I have Lucas Chess and you can play against the computer and adjourn the game. This is nice in case you don't want to finish the entire game in one sitting. Aside from Lucas Chess are there other programs where you can adjourn the game? I can't find any, but this seems like such a simple feature.