Here's a sci-fi action RPG where your inventory is a ship designer and your skills are a tech tree

An indie action RPG  has a cool twist on the genre, having your character as a starship with parts and a crew to be upgraded rather than the normal single warrior and their inventory of random stuff. Starcom: Unknown Space looks like just that, a more low-key but still very enjoyable action take on the space sandbox genre that also blends in narrative events as you land on and explore new planets.

Starcom: Unknown Space calls itself "an action adventure RPG of space exploration, ship building and fast-paced tactical combat" with a "vast open-world universe filled with alien factions vying for power, strange worlds to explore, mysteries to investigate, and a sinister enemy that threatens the galaxy with an ancient power."

So, you know, the normal sci-fi sandbox setup... but with ARPG gameplay. Perhaps like a more chill Starsector.

One of the coolest things in Starcom is definitely the hex-grid that you build your spaceship on. You equip modules, engines, guns, and other parts like they're gear to get your layout right then take the design into combat—with specialties like speedy strike ship, armored battlecruiser, and versatile science ship. At the same time, your "tech tree" of research into new things is also your skill tree, of sorts, letting you choose where to focus efforts as you upgrade the ship.

Part of Starcom is also meeting weird alien factions to trade, fight, and befriend. Their behavior changes based on your own toward them over the course of 60-some story and sidequests across the open world—which, very nicely, you can set an autopilot in to get you back to places you've already been.

You can find Starcom: Unknown Space on Steam.