In my knowledge and limited research Bootswatch was the go to place to find bootstrap themes. I did a post on Bootswatch which you can find here. I have now come to learn of 10 more awesome and unique Bootstrap 4 themes by Alexander Rechsteiner.
These themes are open source, which is obvious because they wouldn’t work without being open source. Each of the 10 themes are unique and have their own style, which gets followed with great consistency. From the dark hacker theme Neon glow to the crisp elegant theme that is Growth. They all follow the same trend and that is to provide a quick, easy theme for your Bootstrap project without you needing to tinker with style code.
True time saver
To grab a theme you like you can simply download the zip file without signing up! It’s no major issue but there is no CDN so you’re on your own if you go down the CDN option.
Its websites and resources like these that have time put in to get good, useable results and really its handy to grab a pre made bootstrap theme to use on your project. It puts the focus back into the core part of your project rather than styling it, which most developers can see this as their downfalls.
Small sample of the themes: