Bookkeeper

Private bookkeeping for rental properties and investments, with your Form 1040 and CT-1040 ready to print.

Download the installer

Free. It installs Python too if your computer needs it, and puts a Bookkeeper icon on your desktop.

Open the file you downloaded, Install Bookkeeper. In Edge or Chrome, click it in the downloads list at the top right of the browser. If the browser asks whether to keep it, choose Keep.
If Windows says “Windows protected your PC”, click More info, then Run anyway.
A window shows the progress. It takes a few minutes, a little longer if Python is installed too. When it finishes, Bookkeeper opens in your web browser, and a Bookkeeper icon is on your desktop and in the Start menu.

Or install by pasting one line into PowerShell

Click Start, type PowerShell, and press Enter.
Copy this line, paste it into that window (Ctrl+V or right-click), and press Enter:
irm https://taxes.decaro.net/install.ps1 | iex

Open Install Bookkeeper from your Downloads folder. Safari unzips it for you; with another browser, double-click the .zip first.
The Mac says it can't check the file. Click Done, open System Settings → Privacy & Security, scroll down, click Open Anyway, then Open.
Terminal opens and installs Bookkeeper. If Python's installer opens, click Continue, Agree and Install, type your Mac password, then click Close. A Bookkeeper icon appears on your desktop.

Or install by pasting one line into Terminal (no security prompts)

Press Command+Space, type Terminal, and press Return.
Copy this line, paste it into Terminal (Command+V), and press Return:
curl -fsSL https://taxes.decaro.net/install.sh | bash

Unzip it, then double-click Start Bookkeeper for your computer (Windows or Mac). It needs Python 3.9 or newer from python.org.

Every release is signed. The installer and Bookkeeper's Check for updates both check that signature, and refuse anything that doesn't match.

Your books stay on your own computer. They're encrypted, and they open only with your password.