Inspired by C418's post from Reddit.
Note: Songs with enharmonic keys are listed both.
Key - Bb minor / A# minor (5 flats / 7 sharps)
Door - F# major / Gb major (6 sharps / 6 flats)
Subwoofer Lullaby - C major
Living Mice - A minor
Moog City - E minor (1 sharp)
Haggstrom - C major
Minecraft - F# major / Gb major (6 sharps / 6 flats)
Oxygene - A minor
Equinoxe - A minor
Mice on Venus - A minor
Dry Hands - C# minor -> F# minor (4 sharps -> 3 sharps)
Wet Hands - A major (3 sharps)
Clark - E Phrygian
Chris - A minor
Excuse - E minor -> D minor (1 sharp / 1 flat)
Sweden - E Dorian (2 sharps)
Dog - Eb Mixolydian (4 flats)
Danny - G major (1 sharp)
Beginning - D# minor / Eb minor (6 sharps / 6 flats)
Droopy Likes Ricochet - C major
Droopy Like Your Face - D minor (1 flat)
Ki - A minor
Alpha - G minor (2 flats)
Dead Voxel - C Phrygian (4 flats)
Blind Spots - Bb major (2 flats)
Flake - C minor (3 flats)
Moog City 2 - E minor (1 sharp)
Concrete Halls - D# minor / Eb minor (6 sharps / 6 flats)
Biome Fest - E minor (1 sharps)
Mutation - Db major / C# major (5 flats / 7 sharps)
Haunt Muskie - D minor (1 flat)
Warmth - D minor (1 flat)
Floating Trees - D# minor / Eb minor (6 sharps / 6 flats)
Aria Math - E minor (1 sharp)
Kyoto - C major -> C minor (no sharps or flats -> 3 flats, parallel key change)
Ballad of the Cats - G# minor / Ab minor (5 sharps / 7 flats)
Taswell - E minor (1 flat)
Beginning 2 - D# minor / Eb minor (6 sharps / 6 flats)
Dreiton - G# minor / Ab minor (5 sharps / 7 flats)
The End - Multiple keys:
Cat - Ab major (4 flats)
Blocks - E minor (1 sharp)
Chirp - C major
Far - D# minor / Eb minor (6 sharps / 6 flats)
Mall - A minor
Mellohi - G Phrygian (3 flats)
Stal - D minor (1 flat)
Strad - F# minor (3 sharps)
Ward - D minor (1 flat)
11 - No key
13 - Unknown
Wait (Where Are We Now) - D# minor / Eb minor (6 sharps / 6 flats)