A good example is the space cadet shift. If I tap left shift, I get an open parenthesis. If I hold it and use any other key, I get a capital letter. It's a lot

A good example is the space cadet shift. If I tap left shift, I get an open parenthesis. If I hold it and use any other key, I get a capital letter. It's a lot nicer than hitting shift+9/0 and I got used to it in about 10 minutes. Any keyboard using the QMK keyboard firmware can do this.