There are 3 repositories under attiny13 topic.
A set of various projects based on ESP8266, ESP32, ATtiny13, ATtiny85, ATtiny2313, ATmega8, ATmega328, ATmega32, STM32 and more.
Simplest ultrasonic ANTISPY voice recording jammer based on ATTINY13 / ATTINY85/45/25 / ARDUINO with PAM8403 / TPA3116D2 module driving piezo ultrasonic transducers (and optionally AD8933 signal generator)
Uninterruptible Power Supply
I²C OLED on an ATtiny10/13/202
T12 Quick Heating Soldering Station
IR Remote Control
OSC Calibrator and High-Voltage Fuse Resetter for 8-Pin ATtinys
ATtiny13 Software UART library.
12-Button IR Remote Control
Simple Logic Probe
IR Remote Receiver and Decoder
A PCI Express card with an inbuilt PWM fan controller and mounting points for an 80mm fan.
Collection of AVR Development Boards
RF Remote Control
High-Voltage Serial Programmer and Fuse Resetter
ATtiny13-based fan control which I use to mod the fan of my Korad KA3005A power supply
Magnetic Door and Window sensor sends open and close code to home automation system
Dimmable USB Night Light with Capacitive Touch Control
Control almost any number of NeoPixels with an IR Remote
Soil Moisture Monitor
It just does bling bling ...
Lightweight WS2812B RGB led driver for the attiny13
Night Light with NeoPixels and Rotary Encoder
In-Circuit Oscillator Calibrator for AVR Microcontrollers
IR Remote Controlled MP3 Player
Tiny Electronic Dice
ATtiny programmer board for use ArduinoUNO as ISP
Simple Candle Simulation
ATtiny13 based PI (Pulse Induction) Metal Detector