There are several popular print-on-demand platforms that specialize in selling custom T-shirts, including: Printful Teespring Redbubble Zazzle Spreadshirt Custom Ink Threadless Society6 These platforms allow you to upload your designs and customize your T-shirts, and they handle the printing and shipping of your products on your behalf. Each platform has its own unique features and pricing structure, so it's important to research and compare them to find the best fit for your business. There are many design software options you can use to create designs for your print-on-demand T-shirts. Here are some popular ones: Adobe Photoshop: a powerful and widely-used software for graphic design. Adobe Illustrator: a vector-based design program used for creating logos, icons, and illustrations. Canva: a user-friendly online platform that offers a variety of design templates and tools. GIMP: a free and open-source image editor similar to Photoshop. Inkscape: a free and open-source vector graphics editor similar to Illustrator. Each of these software options has its own strengths and weaknesses, so it's important to choose one that fits your design style and skill level.