The folks at Tighten:
In this post, I’ll present some strategies we use at Tighten to convert legacy apps to Laravel gradually over time, without needing to perform a full rewrite. Whether you’re upgrading from an old framework or moving to a framework for the first time, following these steps will let you start benefitting from all that Laravel has to offer right away.
What they basically do is set up a new Laravel project and have it catch the parts that they changed/added. Using a catchall rule, all other requests are routed to the legacy code. Clever.
Route::any('{path}', 'LegacyController@index')->where('path', '.*');From then on they start migrating to Eloquent models, introduce some helper functions, etc.
Legacy to Laravel: How to Modernize an Aging PHP Application →