The Minecraft community has always been a driving force behind the game's longevity. For Alpha 1.2.7, modding was still in its infancy, but enthusiasts and developers began creating modifications to enhance gameplay. If you're interested in modding this version, look for community-created resources and forums dedicated to vintage Minecraft mods.
Betacraft Launcher (betacraft.uk) This open-source launcher has a full archive of every Alpha, Infdev, and Indev version.
Starting version. Alpha v1.0.0 (June 30, 2010) Latest version. Alpha v1.2.6 (Dec 3, 2010) Paid. Java Edition version history - Minecraft Wiki