28 liters = 6.16 imperial gallons = 7.40 US gallons. What are the dimensions of the tank? Pretty much all shoaling fish are too small, but depending on the dimensions of the tank it might be alight for a couple of the smallest growing shoaling fish to live in.
Your fish stocking levels would obviously have to be pretty small, but fish & critters which would fit in such a tank at the top of my head would be;
Endlers Livebearers;
http

/www.fishforums.net/index.php?/topic/128756-endler-endlers-livebearer/
Mosquito Fish;
http

/www.fishforums.net/index.php?/topic/253531-mosquito-fish/
Pygmy Corys;
http

/www.fishforums.net/index.php?/topic/104113-pygmy-cory/
African Dwarf Frogs;
http

/www.fishforums.net/index.php?/topic/133204-african-dwarf-frogs/
Ghost Shrimp;
http

/www.fishforums.net/index.php?/topic/198395-ghost-shrimp/
Amano Shrimp;
http

/www.fishforums.net/index.php?/topic/142468-amano-shrimp/
Cherry Shrimp;
http

/www.fishforums.net/index.php?/topic/199872-cherry-shrimp/
Apple Snails & Spixi/Zebra Apple Snails;
http

/www.fishforums.net/index.php?/topic/180470-spixi-apple-snail/
Though not all these fish/critters are suited to a newly set up tank- i would definitely recommend doing a fishless cycle on a tank this small as the ammonia spikes that would happen with fish would happen so rapidly they would be very difficult to control (unless you already have an established mature tank which you can trasnfer some beneficial filter bacteria from the filter from to the new tanks filter (this tank will obviously undoubtedly have to be filtered). The cyling resource information centre, definitely recommended reading

: http

/www.fishforums.net/index.php?showtopic=141944 .