Reelights: always-on (when riding) flashing front and rear lights; magnets mount to spokes, generators mount on fork/stay, wires connect to lights.
Free, if you want to fuss with them 
The fine print:
- front light wire is broken and needs to be spliced
- getting everything mounted just right is a little fussy
- lights worked, but the generator is somewhat prone to getting bumped out of position; so not ideal on a kid’s bike, etc…
- photo shows four magnets, but I found two more, so you could do three magnets per wheel.
