We can use WebIDE for UI5 development nowadays, however for ABAP, it is possible to also use browser to access it ever since so many years ago.
For example, you can access AG3 backend in browser via this link :
https://jerry.sap:44354/sap/bc/gui/sap/its/webguiThe initial screen looks like below, almost exactly the same as what you see in SAPGUI.
All short key like, F3, F8, Ctrl+F3 are still available in browser.
The limitation is that ABAP code highlight is not supported in WebGUI. As a result, if you need to write ABAP code, you’d better to still use SAPGUI or ABAP in Eclipse.
But if your daily work just consists of light-weight operations such as going through customizing via SPRO, checking table content in SE16, or check dumps in ST22, you don’t need SAPGUI at all. See below screenshots for example: