It seems like you’re looking for a stable, robust, open-source note-taking application similar to Lotus Notes, which you enjoyed, and you’ve found Microsoft Power Apps lacking in stability for your needs. Lotus Notes (now HCL Notes) was known for its reliability, collaborative features, and ability to handle complex workflows, so I’ll focus on open-source alternatives that offer similar robustness and stability, particularly for note-taking and potentially app development or customization. Since you mentioned developing an app with Power Apps, I’ll also consider tools that allow some level of extensibility or customization, alongside being free and open-source.

Open-Source Note-Taking Apps Similar to Lotus Notes

Lotus Notes was more than just a note-taking tool—it was an integrated platform with email, databases, and workflow capabilities. The following open-source options may not replicate its full scope but can match its stability and robustness for note-taking and related tasks, with some offering development potential.

1. Joplin

• Overview: Joplin is a widely-used, open-source note-taking app that’s stable, reliable, and supports Markdown for formatting. It’s available on Windows, macOS, Linux, Android, and iOS.
• Why It’s Similar: Like Lotus Notes, Joplin is robust and supports offline use, syncing across devices (via Dropbox, OneDrive, or self-hosted options like Nextcloud), and organizing notes into notebooks. It’s not a full collaboration suite, but it’s highly dependable.
• Stability: Joplin is mature, with a strong community and regular updates, making it a stable choice.
• Customization: It’s open-source (GitHub: joplinapp/joplin), so you can modify the code if you’re comfortable with JavaScript/Node.js. It also supports plugins for added functionality (e.g., tables, better Markdown rendering).
• Use Case: Great for personal or small-team note-taking with a focus on reliability. If you liked Lotus Notes’ structure, Joplin’s notebook hierarchy might feel familiar.

1. Trilium Notes

• Overview: Trilium is an open-source, hierarchical note-taking app designed for building large personal knowledge bases. It runs on Windows, macOS, Linux, and can be self-hosted as a web app.
• Why It’s Similar: Its tree-like structure for organizing notes echoes Lotus Notes’ database approach. It’s robust, supports scripting, and can handle complex note relationships.
• Stability: Trilium is actively maintained and known for being lightweight yet powerful, with no significant stability issues reported.
• Customization: Highly extensible—you can write custom JavaScript within the app to create workflows or features (e.g., automation scripts), somewhat akin to Lotus Notes’ development capabilities. It’s available on GitHub (zadam/trilium).
• Use Case: Ideal if you want a stable, customizable system for structured notes, especially for power users who liked Lotus Notes’ depth.

1. Zim – A Desktop Wiki

• Overview: Zim is an open-source wiki-style note-taking app for Windows, Linux, and macOS, designed for simplicity and stability.
• Why It’s Similar: Like Lotus Notes, it’s dependable and stores data locally in plain text files, making it portable and robust. It supports linking notes, which mimics Lotus Notes’ relational capabilities.
• Stability: Zim has been around for years and is rock-solid, with minimal resource usage and no sync-related instability (though syncing requires external tools like Syncthing).
• Customization: You can extend it with plugins or scripts (Python-based), and its open-source nature (GitHub: zim-desktop-wiki/zim-desktop-wiki) allows deeper modifications.
• Use Case: Perfect for users who want a lightweight, stable alternative with a focus on note organization and linking, similar to Lotus Notes’ database feel.

1. Nextcloud Notes

• Overview: Nextcloud is an open-source, self-hosted cloud platform, and its Notes app provides a simple yet stable note-taking solution. It’s accessible via web, desktop, or mobile apps.
• Why It’s Similar: Lotus Notes was a collaborative platform, and Nextcloud mirrors this with its focus on self-hosted collaboration, including note-taking, file sharing, and more. The Notes app supports Markdown and integrates with the broader Nextcloud ecosystem.
• Stability: Nextcloud is enterprise-grade and widely used, ensuring high reliability when properly set up.
• Customization: As an open-source platform (GitHub: nextcloud/server), you can customize it extensively—add features, integrate with other apps, or even build your own extensions using PHP or JavaScript.
• Use Case: If you liked Lotus Notes’ all-in-one approach and want a free, robust alternative you can host yourself, Nextcloud Notes is a strong contender.

Why Power Apps Might Have Felt Unstable

Since you mentioned trying to develop an app with Power Apps and finding it unstable, it’s worth noting that Power Apps is a low-code platform tied to Microsoft’s cloud infrastructure. Stability issues could stem from network dependency, limited offline support, or complexity in scaling custom apps. The open-source tools above are generally more lightweight, can run locally, and give you full control over the codebase, which might align better with your need for robustness.

Recommendation

• For Stability and Simplicity: Try Joplin first—it’s mature, reliable, and widely praised for its consistency.
• For Customization and Depth: Trilium Notes offers a Lotus Notes-like experience with scripting potential, making it great for power users.
• For Collaboration and Self-Hosting: Nextcloud Notes provides a broader platform with note-taking as a stable component.
• For Lightweight Reliability: Zim is a no-frills, rock-solid option if you don’t need cloud syncing out of the box.

All these are free, open-source, and actively maintained, avoiding the instability you experienced with Power Apps. If you’re comfortable with development, you can fork their repositories and tailor them to your needs, something Lotus Notes developers often appreciated. Let me know if you’d like setup guidance or a deeper dive into any of these!