I made this list by going through the Feature and Foundation modules in SXA for Sitecore 9.3:
Tenant - those marked * are also addable at the Site level.
*Composites (Feature) - adds Composite Theme base template (field) to Settings
Content Validation (Foundation) - adds _HasValidUrlName base template to Page template
Error Handling (Feature) - adds _ErrorHandling base template to site Settings (404 and 500 pages)
*Forms (Feature) - adds WFFM form wrapper, Sitecore form wrapper and Forms Script renderings
*JSON (Feature) - adds JSON Layout at tenant level
Navigation (Feature) - adds Link, Navigation, Breadcrumb, Archive, Link List components
*Redirects (Feature) - adds Redirect as insert option under Home and Page templates
Search (Feature) - adds all the search related features
*Security (Feature) - probably enables the Add Security script
*SiteMetadata (Feature) - adds to pages base templates: Custom Metadata, Open Graph, Seo Metadata, Sitemap, Twitter ,Metadata and settings for Favicon, Robots, Sitemap
Sticky Notes (Feature) - adds Sticky Notes base template to Pages, Page Design and Partial Design
*Taxonomy (Feature) - adds Taggable base template to Pages
Site level - those marked * are also addable at Tenant level and probably have to be added there first.
Accessibility (Feature) - adds Skip links component
Analytics (Feature) - adds Google Analytics rendering
Compliancy (Feature) - adds Privacy Warning rendering
*Composites (Feature) - adds the following components - Accordion, Carousel, Flip, Tabs plus the Snippet rendering
Content Tokens (Feature) - adds Content Tokens folder to site Data folder
Context (Feature) - adds the Site Selector and Language Selector renderings
Creative Exchange (Feature) - adds the CLI theme?
Engagement (Feature) - adds Discus and Facebook Comments renderings
Events (Feature) - adds Event List, Event Calendar renderings and Events data folder
*Forms (Feature) - adds WFFM form wrapper, Sitecore form wrapper and Forms Script renderings
Generic Meta Rendering (Feature) - adds HTML Snippet component
Geospatial (Foundation) - adds Maps Provider, Event Types, POIs settings
*JSON (Feature) - adds JSON Content, JSON List, JSON Results renderings, and CORS settings
Layout Service (Feature) - adds Page layout as JSON rendering
Local Datasources (Foundation) - adds Datasource Configurations to settings
Maps (Feature) - adds Map component
Media (Feature)- adds File List, Flash, Gallery, Image, Media Link, Playlist, Image (Reusable), Video components
Overlays (Feature) - adds Overlays folder under site Home
Page Content (Feature) - adds Title, Page Content, Page List, Pagination, Plain HTML, Promo, Plain HTML (Reusable), Rich Text (Reusable), Rich Text, Field Editor components
Page Structure (Feature) - adds Container, Divider, Splitter (Columns), Splitter (Rows), Toggle, IFrame, Edit Mode Panel components, plus IFrame and Toggle data folders
*Redirects (Feature) - adds Redirects under site Settings
*Search renderings (Feature) - adds all the search related components
*Search settings (Foundation) - adds Facets, Item Queries, Scopes settings folders
*Security (Feature) - adds Login and Logout renderings and Security data folder
*Site Metadata (Feature) - adds Browser Title, CanonicalUrl, Custom, Favicon, Open Graph, Seo, Twitter, Viewport components
Social (Feature) - adds AddThis, Feed, Social Media Share, Twitter components
*Taxonomy (Feature) - adds Tag List, Tag Cloud renderings ; Tags data folder, SxaTags facet