STEM
FunctionForge
Interactive function laboratory — input-output machines, function tables, function tables, and linear functions you build and read on a graph — bridging arithmetic to algebra.
▶ Play it nowBuilt for sittings of about 20 minutes on the screen. That is our design budget, not a measurement.
Meet your mentor
Every Spark & Anvil app has a friendly mentor character that demonstrates, asks, and patiently scaffolds learning. On-device AI personalizes the mentor's responses to your kid's progress — never connecting to a server, never collecting data.
Mentored by Domain
#29B6F6 FunctionForge is a fun math lab where you explore how functions work! You will build "function machines" that take a number in and spit a number out, graph lines on a coordinate plane, and read a graph of motion. It is like having your own math laboratory on your iPad.
Characters who teach
Meet the cast
Each character in FunctionForge is one kind of function: steady lines, staying the same, curves, doubling, rules that switch, undoing, repeating patterns, allowed inputs and outputs, absolute value, and functions chained together.
Stride the Pattern-Walker
Linear functions (constant rate of change)
Read chapter →
Echo the Sameness-Keeper
Constant functions (zero rate of change; output unchanged regardless of input)
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Arc the Curve-Catcher
Quadratic functions (parabola — symmetric rate-of-change-changes)
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Burst the Doubler
Exponential functions (constant *multiplicative* rate of change)
Read chapter →
Pivot the Rule-Switcher
Piecewise functions (different rules for different input ranges)
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Rewind the Step-Reverser
Inverse functions (undoing a rule step-by-step to recover the original input)
Read chapter →
Roundel the Round-Returner
Periodic functions (a pattern that repeats at a fixed interval)
Read chapter →
Sill the Threshold-Keeper
Domain and range (which inputs are allowed and which outputs can appear)
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Vale the Valley-Folder
Absolute value (folding the number line at zero so distance is always positive)
Read chapter →
Weir the Chain-Linker
Composite functions (feeding one rule's output into the next)
Read chapter →
Browse all chapters → · What's distributed-narrative methodology? →
What's inside
Function Machine Lab
Build your own function machines by connecting gears and parts. Drop a number into the machine and watch it transform! Try different inputs to figure out the ru
Graph Canvas
Plot points on a coordinate plane and watch lines and curves appear. Drag points around to see how the graph changes. You will learn about slope, rate of change
Data Lab
Explore real-world data like temperature, sports scores, or animal populations. Place dots on a scatter plot and drag a line of best fit to find trends. See if
Pattern Discovery
Find hidden patterns in number sequences. Once you spot the pattern, write it as a function rule. This is your bridge from playing with numbers to writing real
Mentored by Domain — on-device AI, no data leaves the device.
How FunctionForge handles your kid's data
- ✅ All progress, settings, and AI-generated content stays on the device
- ✅ No analytics, no tracking, no third-party SDKs
- ✅ Free — no ads, no in-app purchases
- ✅ No personal information collected from children — in line with COPPA (updated by the 2026 FTC amendments)
- ✅ No chat with strangers — play-together rooms use a short code and preset emotes, never typed messages
FunctionForge runs on ForgeKit — the open-source Swift Package Manager framework that powers every Spark & Anvil app. ForgeKit ensures consistent accessibility, COPPA compliance, and design language across the portfolio, so your kid's progress and preferences feel coherent across every app they touch.
Coming to the App Store
FunctionForge is in active development. Email us to hear when it ships — no marketing, no spam, just a one-shot launch announcement.
Email me at launch
