One idea for a side project I have (that I lack time for) is an app (or maybe a keyboard, I don't know how far one can push Android's keyboards, but from what I saw it could be quite far) for editing Lisp code. Could be useful with e.g. ECL app, but personally, I'd use that to do quick fixes / small bursts of development while away from home / office.

I was about to ask who edits code on a mobile device, then I remembered a brilliant young coworker of mine who, as far as I could tell, coded exclusively on his iPad when he joined the company. I guess it goes to show you the huge variance of workflows out there.

He transitioned to a laptop soon after joining the company.