I'm making a list of all Opensource DOS/Windows drivers that I'm aware, please feel free to add your own.

DOS:

https://github.com/crazii/SBEMU
https://github.com/Baron-von-Riedesel/VSBHDA
https://github.com/bjt42/softmpu

Windows:

Generic Win9x Display Driver with 3D acceleration made by Michael Dale.

https://github.com/michaeldale/velocity9x

Drivers made by ages2001 (who made the Universal NT Installer - https://github.com/ages2001/Universal-Windows-Installer )

📂 FILE SYSTEM DRIVERS (IFS)

🔹 "BTRFSNT" (https://github.com/ages2001/BTRFSNT) — Btrfs IFS driver for Windows 2000 and XP (x86/x64).

🔹 "EXTNT" (https://github.com/ages2001/EXTNT) — ext1/2/3/4 IFS driver for Windows NT 3.1, 3.50, 3.51, 4.0, Windows 2000, and XP (x86/x64).

🔹 "FATNT" (https://github.com/ages2001/FATNT) — FAT12/16/32 IFS driver for Windows NT 3.1, 3.50, 3.51, and 4.0 (x86).

🔹 "HPFSNT" (https://github.com/ages2001/HPFSNT) — HPFS IFS driver for Windows NT 3.1, 3.50, 3.51, 4.0, Windows 2000, and XP (x86/x64).

🔹 "NTFS3NT" (https://github.com/ages2001/NTFS3NT) — NTFS 1.x/3.x IFS driver for Windows NT 3.1, 3.50, 3.51, 4.0, and Windows 2000.

🔹 "REFSNT" (https://github.com/ages2001/REFSNT) — ReFS IFS driver for Windows NT 3.1, 3.50, 3.51, 4.0, Windows 2000, and XP (x86/x64).

🔹 "UDFNT" (https://github.com/ages2001/UDFNT) — UDF IFS driver for Windows NT 3.1, 3.50, 3.51, 4.0, Windows 2000, and XP (x86/x64).

🔹 "WINUDF" (https://github.com/ages2001/WINUDF) — UDF driver for DOS, Windows 1.0x, 2.xx, 3.xx, 95, 98, and ME.

🔹 "EXFATNT" (https://github.com/ages2001/EXFATNT) — exFAT IFS driver for Windows NT 3.1, 3.50, 3.51, 4.0, Windows 2000, and XP (x86/x64).
💾 STORAGE & DISK CONTROLLER DRIVERS

🔹 "MBRGPTNT" (https://github.com/ages2001/MBRGPTNT) — MBR, GPT, and Dynamic Disk (LDM) support for Windows NT 3.1, 3.5, 3.51, 4.0, 2000, and XP (x86/x64).

🔹 "NVMENT" (https://github.com/ages2001/NVMENT) — Standard NVMe controller driver for Windows NT 3.1, 3.50, 3.51, 4.0, 2000, XP, and Windows 95/98/ME (x86/x64).

🔹 "MMCSDNT" (https://github.com/ages2001/MMCSDNT) — SD/SDHC/SDXC, MMC, and eMMC driver for Windows NT 3.1, 3.50, 3.51, 4.0, 2000, XP, and Windows 95/98/ME (x86/x64).

🔹 "IDENT" (https://github.com/ages2001/IDENT) — Standard PATA/SATA IDE controller driver for Windows NT 3.1, 3.50, 3.51, 4.0, 2000, XP, and Windows 95/98/ME (x86/x64).

🔹 "AHCINT" (https://github.com/ages2001/AHCINT) — Standard SATA AHCI controller driver for Windows NT 3.1, 3.50, 3.51, 4.0, 2000, XP, and Windows 95/98/ME (x86/x64).

🔹 "WINDISK" (https://github.com/ages2001/WINDISK) — IDE, AHCI, NVMe, CD/DVD, SD card, and eMMC driver for DOS, Windows 1.0x, 2.xx, 3.xx, and Windows 95/98/ME.

━━━━━━━━━━━━━━━━━━━━━━

🔌 BUS & INTERFACE DRIVERS

🔹 "USBNT" (https://github.com/ages2001/USBNT) — USB and Thunderbolt 1.1/2.0/3.x/4 support, including hubs, HID, mass storage, cameras, and more, targeting Windows NT 3.1, 3.50, 3.51, 4.0, 2000, and XP (x86/x64).

🔹 "WINUSB" (https://github.com/ages2001/WINUSB) — Universal USB driver for DOS, Windows 1.0x, 2.xx, 3.xx, and Windows 95/98/ME.

━━━━━━━━━━━━━━━━━━━━━━

🔊 AUDIO DRIVERS

🔹 "AUDIONT" (https://github.com/ages2001/AUDIONT) — Generic AC'97, HD Audio, USB Audio 1/2, and Intel SST audio driver for Windows NT 3.1, 3.50, 3.51, 4.0, 2000, and XP (x86/x64).

🔹 "WINAUDIO" (https://github.com/ages2001/WINAUDIO) — Universal HD Audio, AC'97, and Intel SST/DSP sound driver for DOS, Windows 3.xx, and Windows 95/98/ME.

━━━━━━━━━━━━━━━━━━━━━━

🖥️ VIDEO & DISPLAY DRIVERS

🔹 "WINVBE" (https://github.com/ages2001/WINVBE) — Universal VBE/VESA video driver for Windows 1.0x, 2.xx, 3.xx, 95/98/ME, and Windows NT 3.1, 3.50, 3.51, 4.0, 2000, and XP (x86/x64).
⚙️ CPU & SYSTEM DRIVERS

🔹 "WINSIMD" (https://github.com/ages2001/WINSIMD) — CPU SIMD-enabling driver for Windows NT 3.1, 3.5x, 4.0, 2000, XP, and Windows 95/98/ME (x86/x64).

Some other drivers

https://github.com/K4sum1/RTL812X-WinXP
An XP driver for the realtek 8215 2.5Gb NIC made by dietmar over at MSFN forums.

https://github.com/sdz-mods/I217-LM_W98
A working Windows 98 SE network driver for the Intel I217-LM PCH LAN made by sdz-mods (you might have seen some of the custom 3Dfx cards they've made)

https://github.com/sdz-mods/VOPL3
A software AdLib / OPL3 sound chip for Windows 98/ME machines — and an MPU-401 bridge, intelligent mode included by sdz-mods.

If anyone else knows of any more opensource drivers please post in this thread.