Mostly Creative Commons licensed music, including: Instrumental Music for Film & Video (“Find that perfect soundtrack or theme music for your film or video project.”) A lot of tracks, good search (or find) functionality. http://dig.ccmixter.org/
GIMP, the GNU Image Manipulation Program, is an excellent tool for editing images with many features comparable to Adobe Photoshop. It has been around for 25 years and is free and open source. Download: https://www.gimp.org/
Krita is a professional free and open source painting program. It is an excellent tool for concept art texture and matte painters illustrations and comics In addition, is supports 2D animation, and can be downloaded from Krita.org
Free and Open Source yet professionally powerful 2D animation software. Simulates a cell based animation approach, handles bit bitmap and vector layers.
Meshroom is a free, open-source 3D Reconstruction Software based on the AliceVision framework
This powerful photogrammertry tool is available for Windows and Linux
This site lets you create normal maps based on images or a height map NormalMap-Online
Here are two sites with CC0 (public domain) licensed images, one with textures (including bump, normal, roughness, etc) and one with High Dynamic Range Images (HDRI) which you can use to light your scenes. PolyHaven (F.K.A. HDRI Haven & Texture Haven) which also have Models for download
Huge selection of user uploaded sound effects, licensed under Creative Commons Licenses. https://freesound.org/
Make music using the free-to-use audio and video materials from the Library of Congress
This site offers both free (CC licensed) and royalty free (pay once for use right) music.