Translation Management

crowdin.com — Unlimited projects, unlimited strings, and collaborators for Open Source
gitlocalize.com - Free and unlimited for both private and public repositories
Lecto - Machine Translation API with Free tier (30 free requests, 1000 translated characters per request). Integrated with the Loco Translate Wordpress plugin.
lingohub.com — Free up to 3 users, always free for Open Source
localazy.com - Free for 1000 source language strings, unlimited languages, unlimited contributors, startup and open source deals
Localeum - Free up to 1000 strings, one user, unlimited languages, unlimited projects
localizely.com — Free for Open Source
Loco — Free up to 2000 translations, Unlimited translators, ten languages/project, 1000 translatable assets/project
oneskyapp.com — Limited free edition for up to 5 users, free for Open Source
POEditor — Free up to 1000 strings
SimpleLocalize - Free up to 100 translation keys, unlimited strings, unlimited languages, startup deals
Texterify - Free for a single user
Tolgee - Free SaaS offering with limited translations, forever-free self-hosted version
transifex.com — Free for Open Source
Translation.io - Free for Open Source
Translized - Free up to 1000 strings, one user, unlimited languages, unlimited projects
webtranslateit.com — Free up to 500 strings
weblate.org — It’s free for libre projects with up to 10,000 string sources for the free tier and Unlimited Self-hosted on-premises.
Free PO editor — Free for everybody