12. Adjunct professor
Try going back to where it all started: college.
"It can be very gratifying work for people. It's an opportunity for them to share their expertise and mentor a new generation of students," Collamer said.
Teach the next generation of little Einsteins by offering your knowledge.
14. Senior services
As the boomer generation ages, there is a huge opportunity to provide services for them, such as home modification or moving logistics as a senior move manager.
15. Passion projects
Hannon recommended brainstorming a business idea from an existing sport or hobby. She cited the example of a woman who turned her love of sewing into a business making pillows out of old wedding dresses.
16. Tax preparer
Every year, it seems like the tax code gets more complicated with new credits to take and rules to remember. People with tax preparation skills will find their skills in high demand, especially come tax time, and companies like H&R Block stress the ability for their employees to have flexible hours.
17. Pet groomer
The pet business is big and only getting bigger. Pet walkers are another potential encore business opportunity.
18. Professional organizer
Professional organizer and best-selling author Marie Kondo has helped bring professional organization to the forefront.
Facing potentially sky-high legal bills, many opposing parties instead opt for mediation rather than drag disputes out in court. This presents an opportunity for people who have good conflict resolution skills. For more information on becoming one, check out the National Association of Certified Mediators.
Skills like sewing are not as common as they used to be. If you are especially handy in this arena, you might be cut out for a side gig as a seamstress or tailor.
21. Grant proposal writer
Grant writing is highly specialized and can be time consuming, so people who specialize in it can be real value-adds to grant seekers. Check out the Grant Professionals Association for more information.
22. Specialty tour operator
Ideal for people who live near tourist meccas, opening a specialty tour business can help people marry interests in a topic with social interaction and even some exercise.
23. Nonprofit worker
Getting in touch with a nonprofit you already volunteer with or with another whose cause is interesting to you can be a great way to find a fulfilling way to fill the extra hours.
24. Babysitter or nanny
With many families headed by single parents or two-income earners, parents are more time-strapped than ever and reliant on caregiving services.
25. Plant nursery worker
Semiretirees with a green thumb might be interested in this one. Bonus: These jobs can offer outside time, social interaction and exercise.