What Hypersomnia is
Hypersomnia is a top-down arena shooter built around fast, unforgiving fights. It mixes competitive play with pixel graphics and a colorful, atmospheric look. Matches are short and tense, and each duel tends to come down to positioning, timing and reading your opponent rather than soaking up damage. The game is free and open-source, written in bare C++ without a game engine, and it weighs only about 50 MB. You can grab the source from GitHub and modify it however you like.
Playing together with friends
You can set up a one-on-one duel or bring two groups together for a bigger fight. There are two game modes: Bomb defusal, which is team-based, and Gun game, which is free-for-all. On top of that you get 24 unique firearms, 6 magic spells, 4 grenade types and 7 melee weapons, so loadouts and approaches vary a lot between rounds. Before you jump in, pick a faction: Metropolis, Atlantis or Resistance. Each one has its own stance on the conflict running through the game's setting, so it gives your group something to argue about between matches.
Building maps and testing them
The in-game map editor is a WYSIWYG tool, so what you place is what you get. You can host a work-in-progress map and playtest it with your friends in a single click, then keep iterating on it quickly without the overhead of a full game engine. If someone in your group likes making levels, this is where a session can turn into a shared project instead of just another match.
Before you start
Hypersomnia is in Early Access, so expect things to change and rough edges to show up. It's a hardcore arena shooter, which means matches are meant to be demanding and losses are common while you learn the maps and the weapon handling. Online PvP is the way you play with others, so you'll need to be able to connect for matches. The game is free and open-source, and building it yourself from the source is an option if you want to go further than just playing.