I wouldn't call them tools, but Humble Bundle has this.

The one-stop-shop for game devs.

Build your worlds faster and bring your ideas to life with this massive collection of ready-to-use assets for Unreal Engine, Unity, and most major tools by Eldamar Studio. Unlock more than 13,000 assets, including 3D models, effects, UI, audio, textures, graphics, VFX, and more. No matter what kind of game you’re making—whether horror, fantasy, sci-fi, survival, or something completely unique—this bundle has assets for every style and setting. No complicated setup, no use limits—just drop the files in and start creating! Get textures, graphics, VFX, and more, and help support Save the Children!