I use a US QWERTY keyboard, which means I have to jump through hoops whenever I write in French. The best tool I've found for this is QuickAccent from PowerToys: instead of typing a accent and after the letter, it cycles through the available options as you hold the key. With muscle memory, you just know how many times to tap the space bar to write 'é' or 'ê'. It's faster than the macOS accent picker, which requires pressing a number after a long-press.

Since nothing equivalent existed on Linux (and macOS's native solution is clunky), I built one myself using Rust and the Iced GUI framework.