Small indoor citrus plant, sometimes also called Filipino limes. They produce very fragrant white flowers, and small sour but edible fruit that are good for juice and making marmalade. They mature quickly, and start blooming within 2 to 3 years if kept in a sunny south facing window.
First picture is the seedlings I am selling, and second is just to demonstrate a mature plant. I have quite a few available, $5 each or three for $10. Cash at pickup only.