Those names I could find in the database (some of our most activity students did not perform actions in Git/Gerrit/Phab but for example Github or on-wiki which we don't track in our 'technical community metrics' on wikimedia.biterg.io):
author_name:"Nathan_fraignt" OR author_name:"Arcayn" OR author_name:"takidelfin" OR author_name:"Bjornskjald" OR author_name:"Zoranzoki21" OR author_name:"Shreyas Minocha" OR author_name:"Mogmog123" OR author_name:"stibba" OR author_name:"refeed" OR author_name:"stella" OR author_name:"boboquack" OR author_name:"LukBukkit" OR author_name:"Artbarte" OR author_name:"MrSpecjal" OR author_name:"Pipix" OR author_name:"safan41" can be entered as a query on https://wikimedia.biterg.io/ to see how much activity each person had. (Note to myself: In theory names could change due to merging accounts in Hatstall, something to be careful with!)

Please note:

• I collected these names just to check developer retention ("who stays around"): Some folks sometimes wonder if the outcome is worth the efforts put into contests like GCI; whether a name is listed above is completely unrelated to any decision in https://phabricator.wikimedia.org/T204123 who are the winners.
• There obviously might also be activity listed which is not related to any GCI tasks in the time that GCI 2018 was running, just saying for clarity. :)