The best open source alternative to Softaculous is Cloudron, which is both free and Open Source. If that doesn't suit you, our users have ranked six alternatives to Softaculous and three of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Softaculous are BitNami Application Stacks (Free, Open Source) and CapRover (Free, Open Source).
Cloudron is a complete solution for managing apps & users on your own server. Easily deploy production ready apps from the app library and keep them automatically up-to-date. It even comes with a built-in email server and web clients!.
BitNami Stacks make it incredibly easy to deploy your favorite open source software. BitNami Stacks include an open source application and all of the other software necessary to run it, such as Apache, MySQL, PHP or Ruby.
CapRover is an extremely easy to use app/database deployment & web server manager, PaaS, for your NodeJS, Python, PHP, ASP.NET, Ruby, MySQL, MongoDB, Postgres, WordPress (and etc...) applications! Seriously! Who should care about CapRover?