Sentinel Core
Windows, Mac & Linux test builds · source on GitHub Openslot

VarAC-compatible chat, on every computer and phone.

Openslot is an open-source alternative to VarAC that talks to VarAC stations on the air. One program for Windows, Mac, Linux, iPhone, iPad and Android, working with the VARA modem or with XARA, the open-source VARA-compatible modem. Chat, VMail, CQ and beacons from whatever you have with you.

Download for Windows, Mac or Linux Source on GitHub Screenshots
Test builds. The Windows, Mac and Linux versions are ready to try, and the source is on GitHub. Openslot is being tested on the air against VarAC and still changing often. Found a problem? Open an issue or send me an email.
What it is

Cross platform, cross device, VarAC compatible.

VarAC is a great way to chat over VARA, but it only runs on Windows. Openslot speaks the same protocol and runs on Windows too, as an open-source alternative with the XARA modem built in, so you can call a VarAC station from a Windows PC, a Linux shack computer, a MacBook or a phone and they see an ordinary VarAC contact. Every version shares the same core code, so a fix reaches every platform at once.

Works with VarAC

Chat, VMail, CQ calls, beacons, broadcasts, QSY, file transfer, pings and SNR reports, all interoperating with stations running VarAC.

VARA or XARA

Use the VARA modem you already run, on the same computer or anywhere on your network, or use XARA, the open-source VARA-compatible modem, built right into the Windows, Mac, iPhone and Android apps.

Windows, Mac & Linux

A full desktop app with a familiar VarAC-style layout, plus a terminal version. The Windows and Mac apps can run XARA themselves, and on a Mac no Windows machine is needed anywhere.

iPhone, iPad & Android

Native phone apps with Chat, Stations, VMail and Settings tabs, and the desktop's frequency picker and bandwidth buttons on the Chat screen. Plug in a USB audio interface and use the built-in XARA modem, or point the app at a VARA modem in the shack.

Rig control

Hamlib rigctld or direct CAT, so band changes, the band scanner and QSY tune the radio for you.

Logging & contacts

Every QSO logged with ADIF export, an address book filled in from opening reports, heard stations and a built-in user guide.

Screenshots

What it looks like so far.

Openslot on a Mac: the XARA modem bar on top, then frequency and band, Connect Modem, Connect, Call CQ and Send Beacons, Beacons and CQ Calls lists, broadcasts, chat, the QSO bar and the VMail, Broadcast, Send File and Log buttons
On the Mac. The main window, with the built-in XARA modem bar across the top.
Openslot in a QSO with K1DEMO: a beacon and a CQ heard, a broadcast about Field Day files, the chat with the partner typing, SNR readouts and the QSO bar filled in
In a QSO. Beacons, CQ calls and broadcasts heard, the chat with "is typing", and the QSO bar filled in for the log.
The chat grown over the top of the window while the mouse is over it, showing the whole conversation
The whole QSO at a glance. Hover over the chat and it grows to show every message; move away and it shrinks back. New in v0.1.16.
The VMail window with Inbox, Sent, Outbox, Parking and Drafts tabs, an urgent VMail in red and a normal one
VMail. Inbox, sent, outbox, parking for relays, and urgent mail in red.
The BBS File Listing window showing three files on the connected station's BBS
BBS files. List a station's BBS and download what you need.
The CQ slot selector: CQ type, slots 5 to 15 around the calling frequency, and the Call CQ button
CQ on a slot. Pick the slot you'll wait on, as in VarAC.
The QSO Log window with three QSOs, their band, bandwidth, duration and signal reports, and Export ADIF and Import ADIF buttons
QSO log. Every link logged, with ADIF export and import.
The iPhone app's Chat tab: Go on air, a call sign box with Connect, the chat area and the message box, with Chat, Stations, VMail and Settings tabs
Chat. Go on air, connect and type.
The iPhone app's VMail tab with Inbox, Outbox, Sent and Parked folders and one VMail in the inbox
VMail. Inbox, outbox, sent and parked.
The iPhone app's Settings: the Modem menu open with XARA on this phone and VARA on the network
Pick a modem. XARA on the phone, or VARA on the network.
The iPhone app's Settings: profile, modem with bandwidth, host and port, and QSO options such as answering info requests and pings
Settings. Profile, modem and QSO options.

Screenshots from the Mac app and the iOS Simulator (October 2026), and from the desktop app linked to test stations (November 2026; the call signs other than NR5P are made up). The Android app looks much like the iPhone one.

Download · test builds

Get it for Windows, Mac or Linux.

Latest: Openslot v0.2.0 (testing)

Download for Windows Download for Mac Download for Linux Source on GitHub Windows: 10 and 11, 64-bit · Mac: Apple Silicon and Intel, macOS 12 or later · Linux: x86-64 · native programs, no runtime needed

Windows

In PowerShell:

cd $HOME\Downloads
Expand-Archive openslot-v0.2.0-windows-x86_64.zip -DestinationPath . -Force
.\openslot-v0.2.0-windows-x86_64\openslot.exe

On first launch it asks for your call sign. The XARA modem is built in, with a bar above the main window to start it and pick your audio devices; or leave it stopped and use VARA itself, which Openslot can start for you. Test builds aren’t signed yet, so if Windows SmartScreen warns, choose More info → Run anyway.

Mac

cd ~/Downloads
unzip -oq openslot-v0.2.0-macos-universal.zip
xattr -dr com.apple.quarantine Openslot.app   # test builds aren't signed yet
mv Openslot.app /Applications/
open /Applications/Openslot.app

On first launch it asks for your call sign. The first time the built-in XARA modem starts, macOS asks for microphone access: allow it, that's how XARA hears the radio.

Linux

tar xzf openslot-v0.2.0-linux-x86_64.tar.gz
cd openslot-v0.2.0-linux-x86_64
sudo usermod -aG dialout $USER   # serial port access for CAT, then log out and back in
./openslot

Openslot adds itself to your applications menu the first time it runs. Run ./openslot --tui for the terminal version. On Linux it uses a VARA or XARA modem over the network.

Source code

All of Openslot's code is on GitHub at github.com/NR5P/OpenSlot. Read it, build it yourself or report bugs. To build it on Linux: 

sudo apt install build-essential pkg-config libudev-dev libxkbcommon-dev libwayland-dev libgl1-mesa-dev
git clone https://github.com/NR5P/OpenSlot.git && cd OpenSlot
cargo build --release
./target/release/openslot

Source code · README & setup · Release notes & checksums · Report a problem

Status

Where it is.

WindowsTest build available for Windows 10 and 11, with the XARA modem built in or VARA itself.
LinuxTest build available. The desktop app and terminal version, tested on the air against VarAC.
MacTest build available, with the XARA modem built in or any VARA modem over the network.
iPhone & iPadTest builds on an iPhone; tested in the iOS Simulator. XARA built in, or VARA on the network. Not in the App Store yet.
AndroidRunning on a phone, tested over the air against the Mac app's XARA. XARA built in, or VARA on the network. Not in Google Play yet.
SourcePublic on GitHub: github.com/NR5P/OpenSlot.

Openslot is an independent program. It isn't VarAC and isn't affiliated with VarAC or its author. VARA is a trademark of its author; XARA is an independent, compatible modem by x0rro.

Support on PayPal Openslot is made in my spare time. If you find it useful, a tip helps keep it going.