Fully customizable user interface
You can create your own toolbars, add buttons to trigger your preferred or most-used actions. You obtain a bespoke DAW, tailored for your use and needs.
You can also modify REAPER’s theme, create your own or download hundreds of others in the Reaper forum.
Here is below the REAPER 5 official theme
Here are some user-made themes
Kenny Gioia - Customizing the Toolbars
Reaper TV - Creating custom action toolbar shotcuts