A knife sharpener? Kitchen depts are full of 'miracle choppers' but I haven't come across anything yet that gets the stalk & seeds out of either a pepper or a tomato quicker or more neatly than a really sharp blade and a steady hand Plus they usually take ages to dismantle and clean.
I use a Nicer Dicer if I'm doing alot. But it does make small cubes of everything! Great for salsa, or ratatouille pasta sauce. It can deal with tomatoes, but you have to put them in the right way up. Cleans by running under a hot tap.