Socrative has endured over the years as an effective and reliable tool for formative assessment. It can be handy for "quick questions" where you give a verbal prompt and students answer accordingly (true/false, multiple choice, open answer), but you can also create quizzes in advance; they can be teacher paced or have open student navigation. Your "room" can be joined without students having an account, although rosters can be created. (The room number will stay the same, unlike a tool like Nearpod which will change the PIN every time you run a new session.) You can see results in real time and easily export final data. The basic version is free but a Pro version has just been released with more features.