Ha, crossover humour! It's like Core Graphics, which is a Mac thing, only it's chord, because I'm talking about music, but I'm a Mac guy...oh, never mind.
When I'm trying to think of chords in music I always end up with a mental image of a piano keyboard, with the notes that make up the chord pressed. That's all well and good, but I don't have a piano! Apart from some set pieces like barre chords, I can't really think of note combinations in the same way on a guitar, and certainly get flustered trying to harmonise on a violin. What I really need is a piano to sit down and work out harmonies at, which I could then play on the instrument of my choosing (playing a string of notes on any of those instruments isn't so much of a problem).
Unfortunately the biggest piece of floor space I currently have access to is about 1.3m x 0.4m. Maybe some cheap Bontempi would fit there, but not an 88-key upright. If there were a real-space version of the GarageBand digital keyboard, that would certainly fit...in fact it would probably fit in one of my nostrils. One octave doth not a piano make. Some people have suggested Clavinova, MODUS or similar electric pianos before. The thing is, they cost around £2k, whereas an upright is <£500.