Helanthium tenellum 'Broad leaf' is a carpeting grass-like plant that bears close resemblance to a mix between dwarf hair grass and micro swords.  The broad leaf variant has thicker leaves that look almost like Dwarf Sagittaria.  This plant grows by sending out lateral runners just like hairgrass and other swords and when grown under proper conditions can spread to cover the foreground of your aquarium.  For smaller nano tanks, this plant can also serve as a short background plant but adequate lighting and CO2 are recommended.