"Field Lines LITE" lets you put charges on the screen to visualize an electrical or magnetic field. You can watch the field lines or arrows that are showing the direction of the field.
The simulation is using point charges which you can place by drag & drop. The "snap to grid" function helps to make it well-arranged but it can also be turned off.
This app is great if you want (or have) to deal with field lines.
"Field Lines LITE" offers you the same functionality as the full version, but it is limited to 2 charges on the screen.