Asking users to run mongo, es, neo4j, and redis is a tall order. Mattermost just needs (AFAIK) a relational database. Also, less relevant but the Gitlab UI has far too much wasted whitespace. Like 85% of the page is navigation. I like open source competitors to incumbents but maybe just copy Github here - no one is gonna say anything.
Not really. Why? Reddit is opensource but it'd damn hard to setup correctly and start your own instance.