I swear by bodyweight-only resistance / circular strength training. Currently doing TacFit -- despite their ridiculous hard-sell marketing which is uselessly and pointlessly "spec ops" and warrior-themed (I won't link as I'm not affiliated other than a legit happy user). But there are more body-weight approaches than that one. Google circular strength training / CST and much cheaper than buying the TacFit videos would be getting a used paperback copy of "You are your own gym".

It's body-weight only, unlike gyms no machines, unlike crossfit no other weights.

BENEFIT: keep travelling without buying equipment you don't want to carry in your luggage. Don't maintain x gym memberships around the world.

It burns fat (don't really need that too much yet) faster and more efficiently in less time than hours doing aerobic running / swimming / cycling would. Aerobic exercises may be good for heart and lungs, but for calory burning they're laughable.

BENEFIT: muscle building and calory burning in one workout.

(Of course, if you wanna look like The Hulk you'll need to have weights at least kettlebell dumbell or indian clubs, daily protein counting and all the bodybuilding stuff. BUT you will look incredibly impressive with just bodyweight / Tacfit after only 20-30 days of good form, and it only gets better from there -- you even retain a good amount of the goodness after pausing from it up to 2 months afterwards, which a longer hospital attendance may force upon you).

No rep-counting, time-under-tension matters. This matches your bodily clockworks. Your muscles don't count reps either. Time under tension, whether you only get 2 reps under perfect form (important) or 20.

BENEFIT: no counting, just stopwatch.

There are no off-days, you cycle through 4 consecutive days (no intensity day 1: 20 mins, low intensity day 2: 20 mins, moderate intensity day 3: 40 mins, high intensity day 4: 40 mins) all the time. After 4x7 days, it is time to level up, adding sophistication, more challenging movements etc. to keep the body from adapting. TacFit in my view is a pretty unique mix of exercises and movements recombining elements of martial arts, yoga, classical bodyweight exercises and more, that help you on joint mobility, flexibility, core strength, muscle building, posterior improvement and both injury prevention and proofing -- all in a pre-defined package that will last you 9 months in a row without having to customize, modify or tweak the program. Afterwards, add weights, take 5 days off and start from scratch, mix or match, etc.

BENEFIT: minimum time investment gets you results in all areas that matter, including but not limited to mere appearance and looks.

Boy I sound like a marketer but this is really hacker-friendly, entrepreneur-friendly, productive-but-time-pressed-busy-person friendly. It revolves around so much research and experimentation done by the coaches who composed this after decades of experience. They're on Facebook, real people giving sensible advice to everyone and anyone dropping by asking questions. They get 70-80 year old people incredibly fit that couldn't survive neither a gym nor a crossfit session. (But rest assured their exercises are not granny material, they will kick your butt no matter your stage of physical development.) I'm seriously impressed with their stuff. You can browse my past comments here over the last 3 years, I'm not usually writing marketing copy for commercial digital goods around here at all. So this is really simply "everything I need to know about fitness" and I really do think it's the most hacker-suitable option out there.