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.
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.

Demo

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

Install Blender.
Install IfcOpenShell, ensuring that is is compiled to the same Python version and architecture of your Blender installation.
Launch Blender. Open untitled.blend. You should see the export.py script already loaded. Change the hardcoded paths from /home/dion/Projects/blender-bim-ifc/ to wherever you've cloned this repository.
Ensure ifcopenshell is in your Blender Python's path, so that it can import ifcopenshell. You can run sys.path.append('/path/to/your/ifcopenshell/module') in the Blender Python console to do this.
Select all objects that you want to export. Press Run Script, and you will get the results in output.ifc.

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.

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