Simple landing page using Bootstrap
Good start. I would like to add a few minor things:

Character encoding

As a good practice, the character encoding should be the first element of the head section - or at least it should come before the title element:

&lt;meta charset="utf-8"&gt;
&lt;title&gt;SigmaCubes - Home&lt;/title&gt;



  In order for all browsers to recognize a  declaration, it must be
  
  
  Within the &lt;head&gt; element,
  Before any elements that contain text, such as the &lt;title&gt; element, AND
  Within the first 512 bytes of your document, including DOCTYPE and whitespace
  


From Google Code Archive doctype-mirror - MetaCharsetAttribute.wiki

Be consistent

In HTML5 void elements can have an optional / before the closing &gt;. As it seems that you prefer to add this slash, use it everywhere and not only on some elements, like here:


&lt;meta charset="utf-8"&gt;
&lt;meta content="IE=edge" http-equiv="X-UA-Compatible"&gt;
&lt;meta name="author" content="Julian Lachniet" /&gt;
&lt;meta name="description" content="Various HTML and JavaScript projects." /&gt;



Here are some more information about this topic: HTML 5: Is it &lt;br&gt;, &lt;br/&gt;, or &lt;br /&gt;?

Valid HTML

Images have a mandatory alt-attribute:

&lt;img src="img/logo.png" height="32px" alt="Some description" /&gt;


You should add this attribute to all img elements. It will not only help people using screen readers to better understand your website, it might also improve SEO.

For more details, see Wikipedia: https://en.wikipedia.org/wiki/Alt_attribute.

Indentation

Try to indent elements, if possible.  

&lt;a class="navbar-brand" href="#"&gt;
    &lt;img src="img/logo.png" height="32px" /&gt;
&lt;/a&gt;


… is easier to conceive as:


&lt;a class="navbar-brand" href="#"&gt;&lt;img src="img/logo.png" height="32px" /&gt;&lt;/a&gt;



Semantics

Your main navigation looks fine. However, the section starting with &lt;div class="container-fluid"&gt; looks a bit like divitis.

Learn about HTML5 semantics and how to structure the content of your website. Here're some related articles on w3.org to get started:


3.2.1. Semantics
4.3. Sections
4.5. Text-level semantics


Inline styles

Try to avoid inline styles. This might work for a small page like this, but will get complicated as your project grows.


&lt;img class="d-block img-fluid mx-auto" src="img/biglogo.png" style="max-height: 384px; margin: 32px" /&gt;



Instead add a custom CSS file in addition to Bootstrap, where you expand existing styles and add new classes as well.