Today we’d like to introduce you to Louis Deveseleer.
Louis, we appreciate you taking the time to share your story with us today. Where does your story begin?
I’m originally from Belgium, where I studied mechanical engineering. On paper things looked fine, but in my early twenties I was pretty lost and unhappy, without much to look forward to. What turned it around was a simple bicycle. During an exchange year in Munich, I started riding longer and longer trips, and for the first time in ages I felt genuinely good. That was the start of a long detour away from the path I thought I was supposed to follow.
Over the next years I kept chasing that feeling around the world. I did my master’s thesis in Brazil, then rode solo from Belgium to Turkey, 3,000 miles, mostly camping, through 15 countries and a lot of unexpected kindness from strangers. After giving a try to a corporate job, I worked in development cooperation in Rwanda, and then set off on a long, winding trip biking through Europe and Southeast Asia, learning Muay Thai in Thailand and Kungfu in the foothills of the Himalayas.
Somewhere along the way I discovered calisthenics, and it stuck in a way no sport ever had. The trouble was I could never find a good app to guide and track my training, so I decided to build one myself. That became Calistree (https://calistree.com/). I taught myself to code (much of it during Covid), shipped the app, and it slowly grew into something people around the world use every day. What started as a side project became my full-time work in 2024. I still live in Raleigh, where I get to spend my days building the thing I most wished existed. Outside of work I’m still very much a mover: calisthenics, climbing, slacklining, even a bit of Cyr wheel, and I get out to the North Carolina mountains for backpacking whenever I can.
I’m sure it wasn’t obstacle-free, but would you say the journey has been fairly smooth so far?
Honestly, life has been kind to me overall, so I don’t want to overstate the struggle. But building Calistree while holding a full-time job was hard. I spent a whole year just developing the idea (notes, sketches, research) before realizing that paying someone to build the app would cost tens of thousands of dollars I didn’t have. So I taught myself to program and built it myself, one evening and weekend at a time. It’s easy to disappear into a project like that, and keeping some balance in my life took real effort.
The biggest test came when I suddenly lost my job, my only income at the time. Instead of returning to mechanical engineering, where all my experience was, I gambled on software development, where I had none, with just the Calistree prototype to show for it. After plenty of rejections, a small startup took a chance on me, and I built mobile apps for others for a couple of years while Calistree kept growing on the side.
The push to go all-in came from an unexpected place. MacroFactor, one of the best nutrition-tracking apps out there, reached out about hiring me to help build their own workout app. They work with big names in the field, like Jeff Nippard, the #1 weightlifting influencer, and Greg Nuckols of Stronger by Science, so I was excited enough to hand in my notice right away with my employer. In the end we didn’t move forward, because the role would have pulled me away from Calistree and the independence I care about most. But by then I’d already left my job. So I went full-time on Calistree, betting that it would grow sufficiently to support me before I run out of funds – and it worked out! It has grown every year since, and I still own and steer the whole thing myself, which I wouldn’t trade for anything. Looking back, that chain of near-misses was one of the best things that ever happened to me.
As you know, we’re big fans of Calistree. For our readers who might not be as familiar what can you tell them about the brand?
Calistree began as an app for calisthenics and bodyweight training, but it has developed into a full fitness app that now covers weight training, flexibility, yoga, hand- and leg balancing, and indoor and outdoor cardio, which makes it one of the most complete and advanced fitness apps out there.
What sets it apart is under the hood. Most fitness apps hand you a fixed menu of cookie-cutter workouts. Beginners freeze up not knowing what to pick, and more advanced people can’t find something that fits their goals and limits. In Calistree, every one of its 1,700+ exercises is described by dozens of parameters a computer can understand, so the app builds a program around your actual equipment, level, and objectives, and keeps adapting it as you progress. It tracks your workouts in detail and turns improvement into a bit of a game, celebrating small wins so people stay consistent.
The bigger idea is that real, wholesome fitness comes from variety (strength, mobility, balance, cardio), not from doing the same one or two things forever. We understand now how important that mix is, yet almost every app is built around a single discipline. Calistree is growing into the one place that can hold your whole training, understand how it all adds up (your fatigue, your experience, your history), and make smart recommendations from the full picture. That kind of all-in-one app doesn’t really exist yet, and that’s the role Calistree is moving toward. Around 40,000 people use it each month now, and I run it with two collaborators who help me keep pushing it forward.
Can you talk to us a bit about the role of luck?
Mostly good luck, and I try never to forget it. I was lucky in the big, invisible ways first: born healthy, in a peaceful place, to parents who pushed me to try music, sports, and languages, which shaped everything that came later. When I traveled, I was repeatedly helped by the kindness of strangers who had every reason to ignore me and instead took me in.
Even things that looked like bad luck tended to break in my favor. Losing my job felt like the ground disappearing, but it pushed me into software development and, eventually, toward doing what I love full time. Covid, as awful as it was for the world, happened to give me the time to teach myself to code and start Calistree. I’ve worked hard, and I’m proud that the app now supports me and lets me work alongside a couple of great collaborators, but I’m very aware that plenty of hard-working people never get the breaks I did. I just try to stay grateful and make good use of mine.
Contact Info:
- Website: https://calistree.com/
- Instagram: https://www.instagram.com/calistree/
