What's your level? Are you a beginner or do you already have some experience? Also: What's your language, your target market? Suggesting a backend project for

What's your level? Are you a beginner or do you already have some experience? Also: What's your language, your target market? Suggesting a backend project for a frontend language or vice versa doesn't help you much. In general, start with a game. You can be as creative as you like, there are no limits. On the other hand, you can keep it as simple as you feel comfortable. That said, if you have some experience, look for an open source library that needs support. You improve the library, you improve your resume and you will get constructive feedback.