These are some things I've either built in the past or am currently working on.

Rust Web-Assembly Synth
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(Make sure your device is not on mute)

Description: My goal was to get an interesting working example of something using WebAssembly, compiled from Rust. All the AudioContext calling code for this is written in Rust and compiled to WebAssembly with wasm-pack, while the styling (credit to react-piano) and interactivity is handled in React.

A gotcha that I encountered was that in order for Next.js to fetch and load a.wasm file, the Content-Type header must be set to application/wasm. In my case, the wasm file was being served from S3/CloudFront, and had default Content-Type of binary/octet-stream, a limitation of the inner workings of Serverless Next.js CDK Construct. This solution was to use a viewer response CloudFront function to modify the Content-Type header for .wasm resources.
Hexagonal Geospatial Data App
Description: The data for this map comes from GPS Data, via my iPhone. It's POST'd to an API gateway, via a react-native app. Every time my location changes by x meters GPS data is hashed and indexed with Uber's h3, with a default resolution of 0 and stored in DynamoDB. It's then served via CloudFront and rendered here with the help of react-google-maps.

Further styling is done client side, such as map theming and hexagonal heatmap rendering.