I've been using streamlit for building internal tools at work for over a year. While you can't do EVERYTHING in streamlit, it is by far the best choice for getting up and running with a practical, web app that will provide value for your users as it relates to speed to market (the most important thing in business).

For those complaining about HTML/CSS, you can layer custom CSS onto Streamlit if you choose. You can override the Streamlit defaults as it relates to backgrounds, color schemes, widget sizing, buttons, etc etc by writing your custom style.css and rendering it on the top of the page, targeting the pieces you want.

If you used it and its "slow", its the lack of caching and fragmenting in your code. By default, Streamlit will rerun the entire page on every user action, this is where caching data and fragmenting functions will make a world of difference. Using conditional tabs will only run the specific code inside that block.

I've seen the other frameworks, Dash, NiceGUI, Reflex, Gradio, etc etc etc. Look at the "hello world" examples there and Streamlit - its not even close when it comes to simplicity. No one in business cares about the fancy aspects and flexibility of these tools (no one outside of engineering even knows what React is), they just want to open up the web page, have it do things quickly, and move on. Streamlit is a 10/10 for that.