Are there any other projects like "Recruiting app" in salesforce that we can build for practicing admin and developer concepts to gain hands on experience?
As many others mentioned, trailhead is a great way to learn. Other than that, I would suggest taking a look at the workbooks. These workbooks are great step by step guides which walk you through different areas of Salesforce, and personally I found as valuable tools for learning what specifically is needed to pass your certification exams. There are also courses to help you get ready for these exams.
Depending on if you are a hands-on type learner, I would suggest getting your own dev org, thinking of your own app to build, then build it out on your own. This is great experience as you are defining your own requirements, then building it out and testing it. It's a challenge as it might be hard to identify something to build on your own, but this would be a very close 'real world' scenario. Maybe try an event management application.
If you want a less hand-on approach, you can always be active in the communities, SFSE, developer forum, and success community. Being active doesn't always mean answering questions - maybe just look through posts and learn what the question is asking and understanding the answer. This gives insight to other peoples issues which you may encounter some day and helps you understand parts of Salesforce that trailhead and other sources don't always let you dive into. There are also local meetup communities for your to engage and discuss Salesforce. These groups are often run by MVPs or highly engaged Salesforce users. This would get you access to many other users that eat, sleep, and breathe Salesforce as well.
Best way to learn Salesforce is Trailhead - click here
visit , Signup
First go with "Beginner" modules/trails.