There are a number of portland-cement based "leveling" products which can be mixed and poured onto rough concrete to give a smooth surface.
A few things to consider:
1. May need to clean the concrete surface to remove grease and other bond-breaking contaminants.
2. Most are "self-leveling", so if your floor slopes much, may just flow to the low point and out the door.
3. Most are pretty strong, so cracking is not too likely, but talk with the supplier to pick the one that would be best for your used.
And, of course, all you'll end up with is smooth concrete. Then, epoxy, or other durable coating (may wish to add / broadcast onto not-dry paint some sort of sand or other mild abrasive grit - ground-up walnut shells are used by some manufacturers. The rubber tiles, or padded ones for under-foot comfort (maybe only where you walk, not where car drives).