This layout was inspired by qwerty_code_friendly layout.
Having all the symbols accessible without modifiers is a good improvement for coding.
There are only two layouts which is easy to memorize.
There are two "Super shifts", LNUM and RNUM, placed on the most convenient physical keys. Each of them act as shift for the opposite side of the keyboard, and as a modifier key for the current side (usage similar to AltGr in many national layouts). This is achieved by duplicating the corresponding parts of Layer 0 and 1 into Layer 3 and 4. As a bonus, pressing both keys toggles Caps-Lock.
The numerical keypad is composed from regular number keys, works even in macOS.
.--------------------------------------------------. .--------------------------------------------------.
| Grave | ! | @ | # | $ | % | ^ | | TG(1)| & | * | ( | ) | - | Bspc |
|--------+------+------+------+------+------+------| |------+------+------+------+------+------+--------|
| Tab | Q | W | F | P | G | = | | _ | J | L | U | Y | ; | \ |
|--------+------+------+------+------+------| | | |------+------+------+------+------+--------|
| Esc | A | R | S | T | D |------| |------| H | N | E | I | O | ' |
|--------+------+------+------+------+------| { | | } |------+------+------+------+------+--------|
| LShift |Z/LCtl|X/Supe| C | V |B/RAlt| | | |K/RAlt| M | , |./Supe|/ RCtl| RShift |
'--------+------+------+------+------+-------------' '-------------+------+------+------+------+--------'
| LCtl |Super | Alt | [ | ] | | Left | Down | Up |Right | Del |
'----------------------------------' '----------------------------------'
.-------------. .-------------.
| Home | End | | Ins |ScrLck|
.------+------+------| |------+------+------.
| | |PrnScr| | PgUp | | |
| LNUM | Enter|------| |------| Space| RNUM |
| | | Super| | PgDn | | |
'--------------------' '--------------------'
.--------------------------------------------------. .--------------------------------------------------.
| | | | | | <> | | | | | * | ( | ) | - | |
|--------+------+------+------+------+------+------| |------+------+------+------+------+------+--------|
| | F12 | F11 | F10 | F9 | {} | | | = | => | 7 | 8 | 9 | + | |
|--------+------+------+------+------+------| | | |------+------+------+------+------+--------|
| | F8 | F7 | F6 | F5 | () |------| |------| -> | 4 | 5 | 6 | 0 | |
|--------+------+------+------+------+------| | | Enter|------+------+------+------+------+--------|
| | F4 | F3 | F2 | F1 | [] | | | | != | 1 | 2 | 3 | | |
'--------+------+------+------+------+-------------' '-------------+------+------+------+------+--------'
| MUTE | VOLD | VOLU | | | | 0 | , | . | | |
'----------------------------------' '----------------------------------'
.-------------. .-------------.
| | | | | Stop |
.------+------+------| |------+------+------.
| | |Start1| |Start2| | |
| | |------| |------| | |
| | |Play1 | |Play2 | | |
'--------------------' '--------------------'
.--------------------------------------------------. .--------------------------------------------------.
| | | | | | <> | | | TG(1)| & | * | ( | ) | - | Bspc |
|--------+------+------+------+------+------+------| |------+------+------+------+------+------+--------|
| | F12 | F11 | F10 | F9 | {} | | | _ | J | L | U | Y | ; | \ |
|--------+------+------+------+------+------| | | |------+------+------+------+------+--------|
| | F8 | F7 | F6 | F5 | () |------| |------| H | N | E | I | O | ' |
|--------+------+------+------+------+------| | | } |------+------+------+------+------+--------|
| | F4 | F3 | F2 | F1 | [] | | | |K/RAlt| M | , |./Supe|/ RCtl| RShift |
'--------+------+------+------+------+-------------' '-------------+------+------+------+------+--------'
| MUTE | VOLD | VOLU | | | | Left | Down | Up |Right | Del |
'----------------------------------' '----------------------------------'
.-------------. .-------------.
| | | | Ins |ScrLck|
.------+------+------| |------+------+------.
| | |Start1| | PgUp | | |
| | |------| |------| Space|CapsLk|
| | |Play1 | | PgDn | | |
'--------------------' '--------------------'
.--------------------------------------------------. .--------------------------------------------------.
| Grave | ! | @ | # | $ | % | ^ | | | | * | ( | ) | - | |
|--------+------+------+------+------+------+------| |------+------+------+------+------+------+--------|
| Tab | Q | W | F | P | G | = | | = | => | 7 | 8 | 9 | + | |
|--------+------+------+------+------+------| | | |------+------+------+------+------+--------|
| Esc | A | R | S | T | D |------| |------| -> | 4 | 5 | 6 | 0 | |
|--------+------+------+------+------+------| { | | Enter|------+------+------+------+------+--------|
| LShift |Z/LCtl|X/Supe| C | V |B/RAlt| | | | != | 1 | 2 | 3 | | |
'--------+------+------+------+------+-------------' '-------------+------+------+------+------+--------'
| LCtl |Super | Alt | [ | ] | | 0 | , | . | | |
'----------------------------------' '----------------------------------'
.-------------. .-------------.
| Home | End | | | Stop |
.------+------+------| |------+------+------.
| | |PrnScr| |Start2| | |
|CapsLk| Enter|------| |------| | |
| | | Super| |Play2 | | |
'--------------------' '--------------------'