What is NapSac?
NapSac is a free puzzle and thinking game for iOS, Android and the web, based on the knapsack problem from computer science. Players choose items with a value and a weight to maximize total value without exceeding the backpack's capacity.
Is NapSac free?
Yes. NapSac is free to download and play on iOS and Android, with no ads and no real-money purchases.
Who is NapSac for?
NapSac is suitable for players age 8 and up who enjoy logic puzzles, brain training, daily competitions, or competitive multiplayer.
What game modes does NapSac have?
Adventure (60+ puzzles across themed arenas), Daily Challenge (one shared puzzle per day with global leaderboard), Weekly Arena (a new themed arena each week), Time Attack (endless against the clock), ranked Battles (PvP), and asynchronous Friend Challenges.
Pack light. Think heavy.
Your backpack is hungry for treasure. Pack the most valuable items you can without overloading it. Solve puzzles, conquer arenas, battle your friends and take on players around the world.
How It Works
You will learn it in a minute and still be thinking about it a month later. It is built on the knapsack problem, a famous puzzle from computer science.
Meet the Items
Each item has a value and a weight.
Tap to Select
Tap items to drop them in your backpack. Watch the capacity bar fill up.
Watch Your Weight
Find the best combination, but don't go over your backpack's capacity.
Earn Stars
Hit the best possible value to earn stars.
Try It Right Now
This is a real puzzle. Pick items to reach the highest value you can without going over the weight limit. Can you find the perfect solution?
Six Ways to Play
Some days you want a quiet solo run. Some days you want to beat a friend in real time. Both are here.
Adventure
CampaignExplore themed arenas across 320 puzzles. From Grasslands to Summit, every arena gets harder. Beat the boss to unlock the next world.
Daily Challenge
DailyOne puzzle a day, the same one for everyone on the planet. Race the clock, climb the global leaderboard, keep your streak alive.
Weekly Arena
WeeklyA new themed arena every week. Solve them all to capture Naps.
Time Attack
EndlessHow many puzzles can you solve before the clock runs out? A fast endless mode that rewards speed and accuracy in equal measure.
Battles & Challenges
VersusDuel friends and rivals on the same puzzle. Send a challenge they can answer whenever, or climb the ranked ladder from Rookie to Grandmaster.
My NapSac
CollectionSpend the stars you fought for on adorable Nap companions, decorate your world with ponds and trees, and watch your village grow.
Why You'll Love It
Real puzzles that make you think, wrapped in an adventure you'll want to come back to tomorrow.
Train Your Brain
Built on the NP-complete knapsack problem. Every puzzle is its own optimization challenge.
Global Competition
The same daily puzzle for everyone. Fight for the top spot on the worldwide leaderboard.
Battle Friends
Send challenges to friends, take on theirs, and climb the ranked PvP ladder.
Daily Streaks
Solve challenges to build your streak. Reminders are optional and entirely up to you.
Themed Arenas
Travel through Grasslands, Forge, Inferno, Crystal Caves, Summit and the arenas that rotate every week.
Earn Stars & Medals
3 stars for a first-try win, gold medals for a monthly podium. Collect them to unlock new content.
Play Anywhere
Add an account to sync progress across devices. Play offline whenever you like and your scores catch up once you reconnect.
11 Languages
English, French, German, Spanish, Italian, Portuguese, Dutch, Japanese, Korean, Chinese and Russian.
Meet the Characters
Your backpack has many moods. Collect them all in My Garden.
Ready to Pack?
Download NapSac for free and start your puzzle adventure today. Prove you're smarter than a backpack.