IFC4 is a first-class citizen. IFC4 has been an ISO standard since 2013, with the latest published in 2018. It contains many more features than IFC2X3, published back in 2005.
Available for Windows, Mac, and Linux!
Use open-source Blender 2.8 to do digital modeling! Used by NASA, Hollywood, and Ubisoft, Blender allows real-time modeling in rendered view, animations, file linking, proxy objects, Blender Cloud collaboration, lighting analysis, CFD, energy modeling, and a huge ecosystem of add-ons with a thriving community. No licensing, and with a strong Python API to integrate into your custom workflow.
Create complex spatial structures with multiple sites, buildings, facilities, bridges, and building parts. Sites can be broken down into sub-sites and multiple buildings per site. You can categorise different floors to different buildings.
Classify any geometry as any IFC type. Just because it is a wall doesn't mean you should be limited to modeling it in a certain way. Easily change from one type to another, switch relationships and aggregations, reuse or even remove geometry altogether, without damaging your geometry or breaking your BIM model.
Use collections to create element compositions and decompositions with full control over the classifications of their parts. Most BIM programs don't give this flexibility. Create collection instances to efficiently duplicate composite objects.
Allow BIM objects to instance a shared geometric representations. This allows you to place the same shape in multiple objects without drastically increasing your filesize.
Provide a custom value to any simple IFC attribute of an IFC product.
Create product types that regular IFC products can inherit attributes from.
Define your own property sets with control over exactly how the data in the property sets are stored using property set template definitions which you can download or create yourself. Property sets can apply to both types and objects, and object property sets can selectively override type property sets.
Applies array modifiers to create instances.
Basic quantity take-off support for costing.
Settings to toggle export of quantities or geometric representations. Exporting IFC data without geometric representations is much faster and a fraction of the filesize.
Maintain GlobalId between exports, so that you can manipulate the IFC reliably in other software while making changes.
Not all objects need full solid geometry. Create representations as 2D or 3D curves / wireframes for rapid and lightweight BIM development.
Create map conversions and coordinate reference system definitions to link BIM to GIS.
Export basic materials with surface and diffuse colours for representation. You can also link materials to an externally defined file, such as a .blend Cycles material, V-Ray material, or even Radiance material for lighting simulation.
Switch between different types of metric units when modeling.
Model multiple representations for different purposes for a single BIM object or type, such as footprints, axis, reference, or clearance geometry. You can export just the type of representation required for your usecase, or export multiple for the user to choose from.
Record qualitative objectives such as design intentions, health and safety strategies, or code compliance, performance solutions, and more, in the BIM model and directly associate them to objects or types.
Classify objects and types to different classification systems such as Uniclass, Omniclass, or your custom system.
Associate external document files such as plans, brochures, specifications, warranties, or anything to objects and types.
Specify swept solid geometries, allowing you to round-trip geometry manipulation with other BIM software which have more limited geometric tools, like Revit.
Create material layer sets, for objects which have materials in predefined layers with thicknesses.
Create material constituent sets, for objects which are made up of arbitrarily mixed ingredients.
Specify nested and hosted element relationships.
Specify predefined door attributes as defined in the IFC4 specification.
Specify predefined window attributes as defined in the IFC4 specification.
Specify surface styles either defined as part of a material or assigned directly to an object's representation.
Colour coding by IFC class to visually spot mistakes

Some more experimental features:

Cut sections for documentation with OpenCascade
Export gbXML files that are linked to your IFC file to do energy analysis
QA module to generate Gherkin unit tests to validate your BIM models
HTML formatter to generate reports from QA results
COBie spreadsheet extraction to import into CAFM systems

Demo

See demo video

It's only just started, so everything can and will change. But if you want to check it out:

Install Blender 64-bit version.
Download the latest packaged version of Blender BIM from here.
Launch Blender. Go to Edit->Preferences->Add-ons->Install.... Browse to the downloaded .zip file from step 2.
Enable the checkbox next to the Import-Export IFC Blender plugin which will show up.
All done! You will find an import and export IFC option in the File menu.

By default, Blender BIM will export whatever you have selected. The objects you have selected must belong in an IfcProject and spatially contained, such as witihn an IfcBuilding. It must also follow the naming convention. Please see the screenshot below for an example scene.

A naming convention of IfcClass/IfcName is enforced. If you name your object IfcWall/Foo, it will turn into an IfcWall with the name attribute set to Foo. You can override object attributes using Blender's Custom Properties. Your objects must live in a top level Collection defined as a context class, usually something like IfcProject/Foo. You can then nest spatial structures underneath to create a hierarchy.

Pictures

... this Blender files creates this IFC file ...