These days everyone has their favorite mobile apps, ones that make both their personal and business lives run smoother. But are there any apps that are must haves for entrepreneurs and startup founders?

For startup entrepreneurs, it’s crucial to find the apps that actually make a difference to you and your business. Plenty of startup founders are already experts in this area. Heck, apps are the business of many startups these days. But startups in other fields may not be so savvy.

You don’t necessarily need a startup app — most business apps are probably appropriate — but your main concern should be apps that provide enterprise-like power on a smaller scale.

Here are some of my favorite apps that are particularly apt for startups. You may already know and use most of them, but probably not all of them:

The popular Square allows startups and entrepreneurs to accept credit cards from their phones, and is simple to set up. Essentially, the Square Card Reader turns your smartphone into a mobile cash register, which makes it especially useful for consultants, food-truck operators (a booming startup field) and even some traditional retailers. You pay 2.75% per swipe, and the reader accepts Visa, MasterCard, Discover and American Express. Perhaps most importantly, you don’t need to set up a merchant account (which is virtually impossible for startups to do), and there are no additional monthly fees or set-up costs.

If you and your customers use PayPal, check out Bump Pay which easily transfers money between PayPal accounts.

At one point or another, every startup worker has been caught flat-footed needing access to a file on their computer, but that computer is nowhere in sight. DropBox, the hugely popular, simple-to-use cloud-based storage and sharing service, remains the best way to get around this issue. (Both Google and Microsoft have recently introduced similar services.) Once DropBox is installed on your computer, you simply drag and “drop” small or large files, videos or pictures into the Dropbox folder, and they can then be retrieved from any computer or your smartphone. Start with the free version; you can later upgrade to a paid plan if you need additional storage space.

QuickOffice is a suite of apps that let you handle Microsoft Office documents on the Android, iPad, iPhone and Symbian platforms. It will be interesting to see how their recent acquisition by Google will affect the product, although most experts agree the partnership gives both companies an edge in the mobile app market. Check out the site for the plan options, and then you can create and edit documents anywhere you and your phone happen to be.

If you are in need of a mobile sales app, FatStax 2.0 for iPad is a presentation app that lets users browse and present files, including PDFs, PowerPoint slides and video. The app works offline as well, so you don’t need to worry about finding a wireless connection during your sales meeting.

Most techies know (and likely use) Skype, but have you loaded the mobile Skype app? Great for conference calls on the go – just don’t leave it running when you’re not using it (its a battery and bandwidth hog).

If you want to check your website stats, check out Ego, which allows you to quickly view daily, monthly or even hourly visits to your site. You can also see how many people are following you on Twitter and more, all in one place.

What are some of your favorite apps for startups and entrepreneurs? Please share your choices in the comments.