Inspiration
Inspiration usually gives you the chance to re-roll any d20 roll and pick which result you want. It's also a rare and valuable resource (you can only have 1 instance of it at a time). I thought that was boring, so I added a rule on to that.
Marklar's Inspiration: You can only have one instance of this at a time; you either have it or you don't. You can gift it to another player if you would like. It is awarded at the DMs discretion. If you have inspiration, you may use it as a request to bend the rules a little. You pick something that you can't really do (such as an item you didn't actually buy, or a skill you are no good at, etc) and you request that the DM bends the rules for that action, using your point up if approved. Think of it as a "cool point".
EXAMPLE: Had a player who wanted to spit alcohol through a torch to burn a rat swarm. She didn't have alcohol (and that's not how it works anyway) but I allowed her to use her inspiration to make a Dragonborn-style breath attack. Inspiration can also be used in the traditional "roll another d20" manner.
Flanking
When flanking, both creatures get +2 on attack rolls against flanked target.
Flanking requires an ally to be directly across on the other side of an enemy. To determine if you are flanking, draw a line between from you to your ally. If the line crosses the center of the creatures space and both you and your ally are within melee range, both of you are flanking.
NOTE: This rule is OPTIONAL, and is voted upon by players at the start of a game. If this rule is in effect, it applies for both players and NPCs.
XP/Leveling
IF NOT USING MILESTONE, leveling will be based on a 1000XP system. Experience points are almost meaningless after a certain point, because getting 14000 xp out of your needed 45000 makes xp seem worthless. All levels will now require a flat 1000 XP, so that the amount given will be easily understood. For instance, level 8->9 or 1->2 is 1000 XP.
Example: You get 200xp for a difficult fight, 100 for a couple of really good bits of RP, 250 for finishing a quest, and 50 for uncovering some new info. You are 60% of the way to the level, without any obnoxious math involved that arbitrarily goes into the tens of thousands.
Resting (deprecated)
The resting rules as written make things a bit too easy, in my opinion. The rules assume you are going through 3-4 hard combats a day (or 6-8 mediums), but in my games it's more like 1 or 2 hard encounters a day. Because of this, rests are changing slightly. Long rests still recharge your resources, but they no longer heal you to full (that always seemed weird and unnatural to me). Instead, you regain half of your hit dice like normal, then you can spend those to heal like on a short rest. This should make hit die more of a valuable resource, and long rests less like a refresh button without going into "hardcore" difficulty. To summarize:
-Short rests are mechanically unchanged.
-Long rests no longer heal you to full. You gain half your hit die, which you then can spend to heal. Other recovery effects are unchanged (exhaustion, spells, etc.)
NOTE: System was not very popular and confused new players, I have since stopped using it.
Critical Hits
Regular Crits: When you critically hit, you automatically hit the target and roll double dice (including sneak attacks) without doubling the damage bonus.
Marklar's Crits: Since crits are supposed to be special and awesome, if you roll a crit and you roll less than max regular damage, you get at least the base max damage.
EXAMPLE: You crit with a greatsword. Your normal damage is 2d6+2. Your critical hit is 4d6+2. If you roll 4d6+2 and get a total damage of 9, you can replace that and take the MAXIMUM of normal damage (2d6+2) instead, which would be 14 in this case.
SKILLS: Skills do not critically succeed, though over-the-top descriptions will usually accompany such rolls. Any crit or crit fail on a skill check is simply taken for the total amount rolled like normal.
Alignment
I don't like alignments. They're coarse and irritating, they get everywhere! Seriously though, alignments are too black-and-white and restrictive for me. I don't use alignments (5e doesn't do much with them anyway), I just require your character be consistent and realistic. Instead of chaotic good, your character likes to skirt the law to help the poor, since the laws favor the rich. Instead of chaotic neutral, you're a wildcard who makes decisions based on the mood you're in. Much more descriptive, much better than a simple "I am neutral and good".
Main point is that CONSISTENCY is what I am after. Don't think "what does my alignment say I do", think, "What would Steve the Fighter do in this situation?".
Starting Proficiences from Intelligence
Intelligence is a very under-appreciated skill for all except Wizards and Artificers. Under this system, you would get all of your normal proficiencies from race/background/class, except your intelligence bonus would give you some additional proficiencies, reflecting your additional skills from being an intelligent and/or educated adventurer.
After character creation, you get a number of "proficiency points" equal to your Intelligence modifier. You can spend those in the following ways:
Spend 1 point to gain a tool or skill proficiency of your choice (even if it's not a class skill).
Spend 2 points to gain Expertise in a skill or tool you are already proficient in (making Expertise cost 3 points total)
Spend 2 points to gain up to 3 additional languages.\
Increasing your Intelligence through an Ability Score improvement grants one additional proficiency point whenever your modifier increases.
Initiative (Deprecated)
Initiative is a bit of a complicated one. I'm not a fan of the static and unchanging initiative system that is in place, as it seems boring and predictable to me. Plus it makes dexterity even stronger than it already is. At first I used a card system, which was fun, but random and very unpredictable. The system that will be class based. Instead of changing the stat initiative is based on, which can lead to things like an old frail wizard acting before a strong and alert fighter, you will have initiative die based on your class. The dice are as follows:
Rogues and Monks: 1d12
Fighters, Paladins, Rangers, Barbarians: 1d10
Cleric, Bard, Warlock, Druid: 1d8
Wizard, Sorcerer: 1d6
You roll the die for your class (no stat mods) and initiative is resolved as normal.
Monsters receive their own initiative system based on size:
Gargantuan: 1d6-1
Huge: 1d6
Large: 1d8
Medium: 1d10
Small: 1d12
Tiny: 1d12 +1
ROLL20 MACRO: /roll 1dX &{tracker}
Replace the X with the appropriate initiative die, save this as one of your macros, and when rolling initiative, click on your token and then the macro.
NOTE: As interesting and rewarding as I found this system to be, it was a little too confusing for people (especially over roll20). The card system was interesting but usually led to one person taking two turns in a row and another person not having a turn for 10-15 minutes.