Spotted at Leamington, the N gauge layout "Meacham" being set up with the aid of both an electronic spirit level and a real one.
The electronic version is an iPhone app. Lots of similar versions can be downloaded for free for Android phones. I grabbed one ans it really is clever.
As good as the real thing?
Probably. I normally carry my phone with me so I suppose it means I now have a spirit level wherever I go. On the other hand, the real ones are cheap and you can chuck them on the toolbox without worry. Thy come in various sizes too so you can fit them between obstacles or bridge long distances. Most importantly, they tend to be plastic so won't short out your track work if the power is inadvertently applied. Not sure what a dose of DCC juice will do to an iPhone!