A whiteboard with letters of the alphabet along the bottom. Call out a sound and get your child to click the letters to make the corresponding grapheme appear on the whiteboard. If your child knows more than one grapheme for a sound,you might ask him/her to make them all eg ai, a, ay. If your child is finding it hard to remember the new grapheme, you could help by clicking one of the letters and asking him/her to put in the one that goes in front/after.
Below are links to a variety of creative trays you can make and use with your child to help him/her learn to write letters/graphemes. Select one that links to your child's interests or the current time of year, as this should motivate him/her to write. Call out a sound (phoneme) and get your child to write it in the tray.