Micro Machines: The Original Scale Miniatures ("Micro Machines" or "Micros") were a line of toys originally made by Galoob in the mid 1980s and throughout the 1990s. Micro Machines were literally that - tiny scale component style "playsets" and vehicles that were slightly larger than "N scale". Although Micro Machines have not been sold in the United States in some years, newer models are available in the UK and Europe.
Micro machine collecting interest is much smaller than Hot Wheels. It might be considered to be a 1990s item, which some say is not long enough ago to generate adult interest. Some other reasons are that one had to buy a pack at a time, and typically only one would be a new model in any given year, and the toys are smaller and easy to lose. Most sets are worth less than the $5 retail, though some like Civil War can command over $10, and the Aliens set of three are on eBay stores for $50. The rare US version of the action fleet Aliens jump ship has been asking over $70. Some rare Star Trek sets and ships are being sold for $100 to $370 by online auction stores. Some of the hardest to find packages of cars have commanded prices around $100. Those packages often contain prototypes never released to the public. Often large lots can be had for pennies per vehicle on auction sites.
Micro Machines kept sealed in the package take up a lot of space, but ones which are loose don't take up much space at all. One can use one of the original showcases for Micro Machines, or some collectors use fishing tackle boxes to store their collection.
The Micro Machines brand was revived for a few years in response to the popularity of the similar Speedeez brand. Hasbro also opted to use many fantasy castings in the revival. The revival only lasted a couple years. Hot Wheels also had its hand in the trend, releasing their brand known as Atomix (Hot Wheels also produced a brand called Planet Micro in the late 1990s.)
What's it worth? Take a look at this Micro Machines price guide: sold listings for a value indication.