I'm working on a DIY D&D system right now. It's a mash up of every neat thing I've found on the internet while reading OSR blogs over the last few months. Honestly its a kludge and needs to be trimmed back, however, I think a few of the things I've come up with are worth keeping.
The system steals the GLOG magic system pretty much whole-sale, but gives you double the magic dice and has a different spell list (see below).
Some of these spells get a bit algebraic, sometimes using multiple variables to represent multiple costs for one spell. I also use a 'hold' mechanic in these spells that represents maintaining a magical effect by putting a number of dice aside, outside of your dice pool without spending them. When your concentration is broken or you end the effect of your own will, you roll the dice to see if you maintain the magic dice.
Glog Arcane Spells
Charm Person - Increase one person’s reaction to friendly for [dice] x 10 minutes.
Drain Life- You touch a creature. It loses 1/2 [sum] hit points, you gain 1/2 [sum] hit points.
Control Cold- Cover a surface or creature with ice and frost. Either does [sum] damage to one creature and slows movement by 75% (STR save to avoid slow & halve damage), or covers a [dice x 20ft] radius area with slippery ice.
Color Spray- Target is blinded and gains disadvantage on attacks for 1d6 round. If [sum] is higher than remaining hit points, the creature is stunned for an additional round. If [sum] is double remaining hit points, stun for 1d6 rounds.
Enlarge/Reduce- Make a person or object [dice] * 50% larger or smaller.
Reduce Mass- Make a person or person sized object light as a feather for [dice] minutes.
Burning Hands- Flames fire out of your hands in a 10*[dice] foot cone for [sum] damage. CON save for half.
Magic Missle -Fire [dice] * 2 missles from your hand. They may hit any target in your sight and never miss. Each does damage equal to its roll minus 1, to a minimum of 1.
Mending- Return a degraded item back to its original quality.
Sleep- [sum] HD of creatures fall into a magical slumber. WIS save prevents entirely.
Spider Climb- You can walk along any solid surface for [dice] hours.
Prestidigitation -[Hold 1] Create visual and audio effects.
Comprehend Language- [Hold x] You understand one extra language per [dice].
Magic Shield- Any of the following effects
☐ [Hold x] Conjure a shimmering barrier giving you +[dice] AC. Roll any held dice when you are attacked.
☐ As a reaction, prevent [sum/2] damage to any target within 30 ft.
Wizard Sight- Any of the following effects. Each effect requires its own held dice.
[Hold 1] - You can detect magical effects up to [dice] * 30 feet away.
[Hold 1] - You can see through minor illusions.
[Hold 2] - You can see invisible things
[Hold 2] - You can see through magical darkness
[Hold 2] - You can see the true form of shapeshifters
[Hold x] - You can detect the presences of malevolent beings from other worlds up to [dice] * 100 feet away.
Mage Hand- You can manipulate objects with a spectral hand up to [dice] * 30 feet away. You can lift up to [dice] * 5lbs with the hand.
Energy Resistance- [Hold X] - Choose a type of energy (Fire, Cold, Lightning, etc). A target gain Xd6 damage resistance against the chosen type of energy.
Invisibility - You become invisible for [dice] * 5 minutes.
Knock- Acts as a move check of 7 + ( [dice] * 2) on all things fastened, closed, locked, barred, or stuck within a 50 foot radius.
Lock- The reverse of Knock. You close, fastend, lock, bar, or stick one object. It requires a 7 + ([dice] * 2) Move check to open.
Fly - [dice x] creatures gain fly speed equal to your movement speed + ([dice y] * 30) for 10 minutes.
Illusion - [Hold 1] - You create a small or medium sized illusion.
Polymorph- Target changes into a creature that is +/- [dice x] HD from its original HD. The effect lasts for [dice y] hours.
Lightning Bolt- All creatures in a straight line, 100 ft long take [sum] * 2 damage. Anyone touching a target takes half damage. If the bolt hits a metallic surface, everyone touching the surface within 200ft takes half damage (dex save to avoid).
Haste- Target creature adds ([dice] x 15) to their movement speed, gains +[dice/2] to their AC, and has advantage on dexterity saving throws. They also gain [dice/2] additional actions on their turn during combat. The effect lasts 1 minute.
Slow- The target creature halves their movement speed, loses [dice] to their AC and has disadvantage on dexterity saving throws, and can only make one attack on their combat turn.
Fireball- Deal [sum] damage in a 20 foot radius up to 200 feet away.
Dispel Magic- End any magical effect that uses [dice] or fewer dice. Dispel Magic can be resisted by an active magic user by comparing the effect's [sum] to the [sum] of Dispel Magic.
Hold Person- On a failed WIS save, one target person is paralyzed for [dice] * 30 seconds. On a successful save, one limb or body part at the DM's discretion stops operating as normal.
Mirror Image - Create 1d4+dice mirror images. When attacked, randomly determine whether an image, or you, are attacked. The image disappears on a successful attack.
Locate Person- You know the location of a person you have met before within two 6 * [dice] miles (one hex). You know their exact heading and speed.