Minecraft: Pi Edition includes the Minecraft: Pocket Edition Touch UI. MCPI-Reborn includes a mod that enables it. This is enabled by default because the default UI has bad Survival Mode support.
While Minecraft: Pi Edition includes the code necessary for Survival Mode, it is disabled by default. MCPI-Reborn contains a mod that allows you to use Survival Mode. This is always enabled.
Fix Bow & Arrow
Minecraft: Pi Edition has a broken Bow & Arrow. MCPI-Reborn includes a mod that fixes it. This is enabled by default.
Minecraft: Pi Edition disables attacking mobs/players. MCPI-Reborn includes a mod to re-enable it. This is enabled by default.
Minecraft: Pi Edition and Minecraft: Pocket Edition control mob spawning by game-mode. This mod makes mob spawning independent of game-mode. Mob spawning is enabled by default.
Minecraft: Pi Edition doesn't have a functioning settings menu, so it is impossible to enable fancy graphics. This means things like clouds and transparent leaves. MCPI-Reborn includes a mod to enable it. This is enabled by default.
Minecraft: Pi Edition and Minecraft: Pocket Edition both contain auto-jump enabled by default. As many people find this annoying when playing with a keyboard and mouse, MCPI-Reborn includes a mod to disable it. This is enabled by default.
Show Block Outlines
Minecraft: Pi Edition and Minecraft: Pocket Edition control whether to highlight the selected block by UI mode. This mod makes it independent of UI mode. Block outlines are enabled by default.
This mod enables peaceful mode, it is disabled by default.
Minecraft: Pi Edition includes the old non-animated water texture be default. This mod enables the animated version. This is enabled by default.
Both Minecraft: Pi Edition and Minecraft: Pocket Edition include code for smooth lighting that is disabled by default. This mod enables it and is enabled by default.
Both Minecraft: Pi Edition and Minecraft: Pocket Edition include code for 3D anaglyph that is disabled by default. This mod enables it and is disabled by default.
In both Minecraft: Pi Edition and Minecraft: Pocket Edition the Camera entity renderer is disabled. This re-enables it and makes the Camera's particles appear higher so they don't obscure the picture. This is always enabled.
NOTE: This list is incomplete. A updated full feature list can be found at https://gitea.thebrokenrail.com/TheBrokenRail/minecraft-pi-reborn/src/branch/master/launcher/client-data/opt/minecraft-pi-reborn-client/available-feature-flags
Reborn got a major updater on June 17, rehauling much of the codebase to add new features, like finally the removal of Docker as a dependency, which allowed reborn to finally be run on Windows systems via WSL2 and GWSL (broken as of now due to dropped support for Debian Buster). Docker was also removed as a depend on x64 linux systems as well, instead using a custom media layer proxy to forward the calls to GLFW and having the binary run with QEMU. Other notable changes included sound support, ARM64 support, External Server support instead of a proxy, and binding the Q key to drop items.
MCPI-Reborn also has it's own server software with things like survival mode support and mob generation designed to replace the aging pocketmine software which was the only server option for MCPI, leveraging MCPI's LAN server function and RakNet's WAN server connection. More info can be found at https://gitea.thebrokenrail.com/TheBrokenRail/minecraft-pi-reborn#dedicated-server.