there are no equivalents as sky+ is exclusive to their boxes. however, a lot of linux satellite receivers do have facilities for using an EPG and adding a HDD. with those you can record programs, and pause/rewind live TV just as you would with sly+ vu+ and dreambox are about the best for this.
to be honest i havent used sky+ for years so i dont know what improvements or extra features it might have. i suppose if all sky+ does is, record programs when you want, pause/rewind live TV, then yes it does. sky+ is probably the best there is because it was designed that way, but other boxes like those i named above do some of the same things and other things besides that a sky+ cant do.