BetterJPEG allows applying operations to multiple images at once. To do this:
1) Select images you want to apply an action to by clicking on the corresponding thumbnails in the browser pane. Hold the Shift key down while clicking on thumbnails to select a continuous range of images, or hold the Ctrl key down to add/remove images to the selection in a one-by-one fashion.
2) Apply the action to selected images.
Note: Batch operations can only be undone for current image. In general it is recommended to work on copies of images and keep the originals untouched.