Launch an event planning and management service that specializes in organizing events such as parties, corporate meetings, and small weddings. Offering tailored packages that include venue selection, catering, decoration, and entertainment can help cater to different budget levels. Building a network of reliable vendors and venues will be crucial for providing quality service.

Start a subscription box service that caters to niche markets such as healthy snacks, self-care products, or art supplies. Each month, subscribers would receive a curated box of high-quality products that fit their interests. This business model encourages recurring revenue and customer loyalty, with the potential for growth through partnerships and collaborations.

Offer tech support and IT services targeted at young adults and small businesses. Common services could include setting up and maintaining websites, troubleshooting hardware and software issues, and providing cybersecurity consultations. Expanding into offering basic coding and tech-literacy workshops can also attract a broader customer base.

Create a business that sells customized craft and art goods such as handmade jewelry, personalized stationery, or custom prints. Marketing can be done through social media platforms like Instagram and Etsy, where visual appeal plays a significant role. Offering seasonal and themed items can help capitalize on different times of the year.

Develop a fitness and wellness coaching business targeted towards young adults. This can include personalized workout plans, nutrition advice, mental health support, and lifestyle coaching. The service can be offered through online platforms, allowing for virtual coaching sessions, progress tracking, and community support forums.

Offer freelance writing services for businesses, blogs, and publications. This could range from creating SEO-friendly blog posts to writing in-depth articles, business reports, and social media content. Building a portfolio and networking with potential clients through freelancing platforms will help in establishing credibility and gaining steady work.

Start a business focused on developing mobile applications for various purposes, such as productivity, entertainment, or education. The service could cater to businesses looking to create apps for their customers or develop unique standalone applications that solve everyday problems. Offering end-to-end solutions from concept to deployment will add extra value.

Form a digital marketing agency that helps small businesses improve their online presence. Services can include social media management, search engine optimization (SEO), content creation, and online advertising campaigns. The agency can offer tiered packages to suit different budgets, along with analytics and performance tracking to show clients the effectiveness of their campaigns.

Create a fashion brand that focuses on eco-friendly materials and ethical production methods. This could involve upcycling old clothing, using organic fabrics, and ensuring fair trade practices. The business can also promote a buy-back program where customers can return old clothes for a discount on future purchases. Marketing can focus on the brand's commitment to sustainability and its impact on the environment.

Launch a platform where young adults can offer tutoring services in subjects they excel in. This can be done through live video sessions, recorded lessons, or even personalized study plans. The platform could include features like scheduling, payments, and feedback systems. Additionally, tutors can offer specialized sessions for exams like SATs, ACTs, and college entrance tests.