The sites below have useful information about clinical trials in general. For info about specific trials for ALS, see the page Specific Treatments .
clinicaltrials.gov - the definitive site for clinical trials running under the US Food & Drug Administration (FDA): https://clinicaltrials.gov/
I prefer to use the "Advanced Search": https://clinicaltrials.gov/ct2/search/advanced?cond=&term=&cntry=&state=&city=&dist=
Here's an example search (Only showing phase 2 or phase 3, interventional trials, that are currently recruiting or not yet recruiting): https://clinicaltrials.gov/ct2/results?cond=Amyotrophic+Lateral+Sclerosis&term=&type=&rslt=&recrs=b&recrs=a&age_v=&gndr=&intr=&titles=&outc=&spons=&lead=&id=&cntry=&state=&city=&dist=&locn=&phase=1&phase=2&strd_s=&strd_e=&prcd_s=&prcd_e=&sfpd_s=&sfpd_e=&lupd_s=&lupd_e=
For help using this site, see: this help page
ALS TDI has a copy of the info from clinicaltrials.gov, but filtered to include only trials related to ALS, and their search and display of information can sometimes be more helpful. For example, they color-code the recruiting status, and allow you to search for trials at sites close to you. https://www.als.net/als-research/als-clinical-trials/
You can also subscribe to their emails sent periodically with info about updates to clinical trials: https://www.als.net/subscribe/
Webinar about findng trials for ALS: https://www.neals.org/for-people-with-als-caregivers/educational-webinars/simplifying-the-search-how-to-find-the-right-als-clinical-trial-for-you
I Am ALS has a copy of the info from clinicaltrials.gov, but filtered to include only trials related to ALS: https://iamals.org/alssignal/