It also makes it easy for developers to port .NET applications created with Visual Studio to Linux and macOS maintaining a single code base for all platforms.


Supports Linux, Windows and macOS.

Advanced Text Editing

Code completion support for C#, code templates, code folding.

Configurable workbench

Fully customizable window layouts, user defined key bindings, external tools

Multiple language support

C#, F#, Visual Basic .NET, Vala

Integrated Debugger

For debugging Mono and native applications

GTK# Visual Designer

Easily build GTK# applications


Create web projects with full code completion support and test on XSP, the Mono web server.

Other tools

Source control, makefile integration, unit testing, packaging and deployment, localization

What's New:

Previous Notes:

  • Various bugfixes

Resolved Issues

  • 10643 [System.Windows.Forms] Combobox SelectedIndexChanged when mouse move
  • 10651 Missing memory barrier with some atomic operations
  • 12022 Form closes although its DialogResult is manually set to None
  • 15418 nuget: ThreadAbortException in SchedulerThread
  • 15612 [sdb] Runtime crash when accessing invalid address under debugging
  • 16243 LLVM: bound checks are not eliminated for simple cases
  • 16623 Hebrew and other non-Gregorian calendars are broken
  • 16763 Bump F# to 5.0
  • 16969 [coop][interp] two failing tests with checked-build=gc
  • 17869 Assertion failure with default interface method
  • 17881 .NET 4.5 console app bundled with mono 6.4.0 cannot be signed, or crashes when run
  • 17980 The UseColumnTextForLinkValue field of DataGridViewLinkColumn does not work
  • 18009 patch to build on FreeBSD/PowerPC64
  • 18019 WinForms ContextMenu gets stuck open if you middle-click
  • 18020 WinForms RadioButton auto-check still occurs when AutoCheck = false
  • 18030 mono-io-layer-error (-1) exception on Android with Mono6.4 and AdGuard used
  • 18061 [interpreter] Conversions.ToX(NaN) are expected to throw OverflowException
  • 18064 PowerPC linux build is broken
  • 18106 “No compatible code running” after repeated breakpoint in Android.OS.AsyncTask.RunInBackground() On android sometimes there is no valid_info but the ctx is valid and the debug can continue. (#18463)
  • 18120 Roslyn fails with interpreter
  • 18127 bug: mini_get_shared_gparam get wrong MonoImage?
  • 18191 Mono crashes on attemp to evaluate ‘ref’ returning method with debugger
  • 18202 Failure to build and run testsuite under muslc
  • 18213 Some unit tests (e.g. mscorlib) are too big to run in every configuration and needs to be split
  • 18323 Error MT2101: Can’t resolve the reference ‘System.Security.Cryptography.Pkcs.SignedCms’
  • 18339 Mono crashes when loading a video file from Subtitle edit
  • 18364 Incorrect Reflection & TypedReference behavior in AOT mode.
  • 18370 ThreadLocal not using the JIT fast path for TLS access
  • 18417 LLVM JIT omits frame pointer even if MONO_DEBUG=disable_omit_fp is set
  • 18418 Thread.VolatileRead(ref Object) causes assertion failure
  • 18506 [WinForms] Invisible ComboBox controls can still pop up their lists if a ContextMenu is displayed
  • 18524 Missing Tatar CultureInfo tt and tt-RU
  • 18530 Mono Interpreter Losses some Command Line Arguments to Microbenchmarks
  • 18554 [autotools] Weak -mminimal-toc testing causes fallthrough
  • 18560 [2019-12] [iOS] [armv7] undefined symbol ___multi3 on Release (LLVM) Bump external/llvm-project to 2ca761dc8b83a75ad950f468fb68e764e61d9cfa (#20365)
  • 18572 Performance regression since Switch to CharUnicodeInfo from corefx
  • 18584 [wasm][debugger] DebugProxy Faults on Refresh w/ JS Breakpoints
  • 18612 [ios][32bits] Assertion at /Users/builder/jenkins/workspace/archive-mono/2019-12/ios/release/mono/mini/aot-runtime.c:5237, condition `plt_entry’ not met
  • 18646 [wasm] Blazor - CSB iOS 13.3 “Maximum call stack size exceeded” error is still happening.
  • 18675 Failure to build with AOT disabled
  • 18794 [coop] assertion when socket_transport_send called from the crash reporter
  • 18826 codesigned mkbundled executable never ends with xmonkeysloveplay
  • 18827 bug-10127.exe runtime test hangs on Windows C++
  • 18917 Explicit interface property ignored when there is a default implementation
  • 19005 Console finalized before any objects writing to it have finished
  • 19009 Crash in mono_create_specific_trampoline on iOS 64-bit/32-bit + tvOS
  • 19136 [merp] Unnecessary call to msync in mono_state_free_mem
  • 19377 Request: please make mono_type_get_name_full a public symbol
  • 19389 [iOS] libmonosgen-2.0.a is leaking symbols
  • 19393 [sdks] runtime doesn’t link with Xcode 11.4 due to weak import symbol ___darwin_check_fd_set_overflow
  • 19451 WatchOS: HttpClient.PostAsync throws “System.NotSupportedException: This method contains IL not supported when compiled to bitcode”
  • 19492 Debugger crash when inspecting element
  • 19784 Running llvm/ in a WSL environment will segfault
  • 19860 mac/iOS: SIGSEGV will hang the process, not terminate it
  • 20107 Sigsegv in libmacho.dylib getsectbynamefromheader_64
  • 20138 Segmentation fault when AOTing customer application
  • 20275 Xamarin.Android Designer Crashes with mono/mono/2020-02@66e2b840
  • 20490 [Bug] The app crash with native exception when changing visibility of Grid
  • 20533 Unknown opcode float_conv_to_i when building Xamarin.iOS project with FSharp.Core 5.0.0 dll
  • 8709 ProfilerTests.MonitorEventsAreRecorded and ProfilerTests.HeapshotDataIsValid are flaky
  • 8806 gdb warns about our llvm6.0 fullaot dwarf data (linux) Emit DWARF debug_abbrev offset for compile units as a label instead of 0 (#19794)
  • 9726 DataGridViewImageColumn ImageLayout property zoom doesn’t work