ABOUT
About PETRA
PETRA is the projection tool Threshing Floor of City (TFoC) built for church gatherings: lyrics, Scripture and media stay on the big screen, so the team can focus on serving instead of fighting the software.
WHAT IT DOES
What it does for you
Line up a whole service in one flow
Songs, Scripture, images, video and notes go into one project in order; output and preview are split so each volunteer knows their job and nobody is juggling windows.
Hymns and Scripture built in
A hymn library and all 66 books of the Chinese Union Version ship with the app; search by title, lyric, book or chapter and insert in one step — no panic hunting for a song on the spot.
Backgrounds and templates out of the box
Image and video backgrounds, covers and templates ship with the app, so there is no extra asset hunting. Solid-color and image backgrounds are included in the Free tier.
Anything you can project onto
Widescreen, standard and portrait output: projectors, TVs and vertical screens each get the right format, so you never rebuild content for a room.
The room and the stream, one picture
The virtual camera lets Tencent Meeting, DingTalk and other meeting apps take the projection directly; NDI output feeds a switcher, so the online congregation sees what the room sees.
Works when the network does not
Everything runs locally. Flaky venue Wi-Fi or server maintenance never stops the service.
PRINCIPLES
What we stand for
Offline first
Projection runs entirely on your machine. When the network fails, the service goes on — that is a design baseline, not a bonus feature.
Core features stay free
The Free tier's core projection is free forever. Pro adds video backgrounds, media playback, PPT import, widgets and streaming, currently free for a limited time; Max is coming later. See pricing.
Your data stays local
Projects, songs and assets stay on your own computer; we never receive or store your service content.
PRIVACY
Privacy: we only care whether it works
- We don't touch your content: projects, songs, Scripture and assets live on your computer — we cannot see them, and they are never uploaded.
- We count anonymous events only: the client reports whether a notice was shown or clicked, using an anonymous identifier; those numbers cannot be traced back to a person.
- Notices are product notices only: version updates, maintenance notes and feature launches — no ads, no marketing pushes.
- It works without the network: block every request and projection still works as usual.
DEVELOPER
Developer: Threshing Floor of City
Threshing Floor of City (TFoC)
Threshing Floor of City is a fellowship that watches, worships and works for God in the city.
On the name "threshing floor"
A threshing floor is where grain is threshed, winnowed and gathered. We are a group of workers who have committed to serve God on His threshing floor: watching and praying among people, worshipping Him, and being faithful in everyday work.
What we do
Rooted in worship and prayer, we serve churches and their volunteers in the city: watching over one another, worshipping together, and offering the tools and experience we have so that serving becomes lighter.
Why we built PETRA
The app came out of a real need in our own gatherings — projection kept getting in the way. Someone had to build it properly, so we did, and we give it to churches for free.
THE NAME
The name PETRA
PETRA comes from the Greek πέτρα, meaning “rock”. In the biblical tradition, “rock” was first a title reserved for the LORD in the Old Testament, expressing who He is — eternal, faithful, saving, a refuge (Deut 32:4; Ps 18:2). The New Testament turns this image toward Christ: Paul says plainly that the rock which followed Israel in the wilderness “was Christ” (1 Cor 10:4), and Peter, quoting Scripture, calls Him “the cornerstone” (1 Pet 2:4–7). The rock — petra — therefore points to Jesus Christ, the one unshakable foundation of the church.
PETRA takes its name from this. Our prayer is that the Lord would be pleased to use this tool to help churches worship, learn and proclaim the gospel more faithfully — and that all the glory would be His.
CONTACT
Contact and feedback
Product and updates
Release notes live in the changelog; download, verification and system requirements are on the download page.
Feedback
Hash mismatch, SmartScreen trouble, feature ideas or usage questions — email us: michaelkuo@foxmail.com
About this website
This site holds the product introduction, downloads and release notes; the app also reads one startup notice covering versions and maintenance only.