CoachApp pro helps me a lot! From their website:
Personal Trainer business app
Coach App Pro simplifies Coaches and Personal Trainers’ Administration work. track your clients, their orders and payments for free!
I can answer the first part of your question: “What apps help you run your business more effectively?”
I love Evernote. I don’t just use it to help run my yoga business more effectually. I also use it to manage run my personal life more effectively. It’s by far the most useful “tool” I’ve come across and I use it every day [e.g. managing clients, managing prospects, managing travel/holidays, writing a book (create a note for each chapter), writing blog posts, etc]. The best part is that you can sync all your “notes” across all your devices (smartphone, tablet, computer). Before becoming a full-time yoga teacher I was a business consultant and used to recommend Evernote to all my clients.
Millions of people all over the world use Evernote. The free version is great. I recently upgraded to the paid version which has a few advanced features such as ability to share “notes” with other people. You can find out more here: https://evernote.com
BWY Yoga Teacher
Free yoga lesson planning tips & tools | http://GeorgeWatts.org