The EEW Lazy Kate holds bobbins while you ply them together.  It comes with three pieces so it can hold three bobbins at a time.  Here is a list of some of its most impressive features:

• Magnetic locking system firmly holds each piece together.
• The base can be separated and weights added if you want a heavier base.
• Both 3/8 inch (9.5 mm) and 1/4 inch (6.3 mm) rods are included to make it work well with all EEW Nano/6 bobbins and many bobbins from other wheel manufacturers.
• Yarn spikes can be put through yarn balls and then this will let you unroll the yarn ball without it tangling.
• Rods unscrew and bases stack together, making this extremely portable.
• Includes stoppers to prevent bobbins from falling off, and a braking system.